WO2013018234A1 - Exhaust purifying apparatus for internal combustion engine - Google Patents
Exhaust purifying apparatus for internal combustion engine Download PDFInfo
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- WO2013018234A1 WO2013018234A1 PCT/JP2011/067998 JP2011067998W WO2013018234A1 WO 2013018234 A1 WO2013018234 A1 WO 2013018234A1 JP 2011067998 W JP2011067998 W JP 2011067998W WO 2013018234 A1 WO2013018234 A1 WO 2013018234A1
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- fuel ratio
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- ratio sensor
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- exhaust gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
- F01N3/0885—Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9413—Processes characterised by a specific catalyst
- B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9495—Controlling the catalytic process
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- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
- F01N3/0842—Nitrogen oxides
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2006—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating
- F01N3/2033—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating using a fuel burner or introducing fuel into exhaust duct
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- F01N9/00—Electrical control of exhaust gas treating apparatus
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- B01D2251/00—Reactants
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- B01D2251/208—Hydrocarbons
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- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/90—Physical characteristics of catalysts
- B01D2255/91—NOx-storage component incorporated in the catalyst
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2510/00—Surface coverings
- F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
- F01N2560/025—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting O2, e.g. lambda sensors
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/04—Methods of control or diagnosing
- F01N2900/0416—Methods of control or diagnosing using the state of a sensor, e.g. of an exhaust gas sensor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/0601—Parameters used for exhaust control or diagnosing being estimated
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1612—SOx amount trapped in catalyst
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present invention relates to an exhaust purification device for an internal combustion engine.
- the engine exhaust passage, NO X storage catalyst air-fuel ratio of the inflowing exhaust gas when the lean that releases NO X air-fuel ratio of the exhaust gas which is occluded becomes rich for occluding NO X contained in the exhaust gas inflow was placed, NO fuel addition valve disposed in the X storage catalyst in the engine exhaust passage upstream of the air-fuel ratio sensor arranged in the NO X storage catalyst downstream of the engine exhaust passage, NO based on the output signal of the air-fuel ratio sensor
- An internal combustion engine in which the air-fuel ratio of exhaust gas flowing into the X storage catalyst is feedback controlled to a target air-fuel ratio is known (see, for example, Patent Document 1).
- this air-fuel ratio sensor gradually deteriorates when exposed to high-temperature exhaust gas heat for a long period of time or when it is poisoned by HC in the exhaust gas. As a result, the air-fuel ratio detected by the air-fuel ratio sensor becomes lower. It is known that the actual air-fuel ratio is not accurately represented. However, SO X is contained in the exhaust gas. In this case, the air-fuel ratio sensor is considered to be affected by this SO X. However, it has not been known at all how the air-fuel ratio detected by the air-fuel ratio sensor is affected by SO X contained in the exhaust gas.
- An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that detects sulfur poisoning of an air-fuel ratio sensor based on the found relationship.
- an internal combustion engine in which an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas is disposed in the engine exhaust passage and exhaust purification control is performed based on the air-fuel ratio detected by the air-fuel ratio sensor.
- the air-fuel ratio sensor has a solid electrolyte, electrodes that cover both sides of the solid electrolyte, and a diffusion resistance layer that covers one of the electrodes, and exhaust gas is guided onto the diffusion resistance layer.
- Air-fuel ratio sensor by the exhaust purification system of an internal combustion engine to detect the sulfur poisoning amount of the air-fuel ratio sensor from a change in the air-fuel ratio detected is provided for.
- the sulfur poisoning amount of the air-fuel ratio sensor can be detected.
- FIG. 1 is an overall view of a compression ignition type internal combustion engine.
- FIG. 2 is a view schematically showing the surface portion of the catalyst carrier.
- FIG. 3 is a view for explaining an oxidation reaction in the exhaust purification catalyst.
- FIG. 4 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- Figure 5 is a diagram illustrating a NO X purification rate.
- 6A and 6B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
- 7A and 7B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
- FIG. 8 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 9 is a diagram illustrating a NO X purification rate.
- FIG. 10 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 11 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 12 is a diagram showing the relationship between the oxidizing power of the exhaust purification catalyst and the required minimum air-fuel ratio X.
- FIG. 13 is a graph showing the relationship between the oxygen concentration in the exhaust gas and the amplitude ⁇ H of the hydrocarbon concentration, where the same NO x purification rate can be obtained.
- Figure 14 is a diagram showing a relationship between an amplitude ⁇ H and NO X purification rate of hydrocarbon concentration.
- FIG. 15 is a diagram showing the relationship between the vibration period ⁇ T and NO X purification rate of hydrocarbon concentration.
- FIG. 16 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
- Figure 17 is a diagram illustrating a map of exhaust amount of NO X NOXA.
- FIG. 18 is a diagram showing the fuel injection timing.
- FIG. 19 is a diagram showing a map of the additional fuel amount WR.
- 20A and 20B are views showing a hydrocarbon injection period and the like.
- 21A and 21B are time charts showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- 22A and 22B are views showing the structure of the air-fuel ratio sensor shown schematically.
- FIG. 23A and 23B are diagrams showing changes in the air-fuel ratio detected by the downstream air-fuel ratio sensor.
- FIG. 24 is a diagram showing a map of peak air-fuel ratio.
- FIG. 25 is a time chart showing changes in the peak air-fuel ratio reduction rate.
- 26A and 26B are diagrams showing changes in the air-fuel ratio detected by the downstream air-fuel ratio sensor and the like.
- FIG. 27 is a time chart showing changes in the peak air-fuel ratio reduction rate and the like.
- FIG. 28 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
- FIG. 29 is a diagram showing a change in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- 30 and 31 are flowcharts for performing operation control.
- FIG. 32 is a flowchart showing an embodiment of a peak air-fuel ratio detection routine.
- FIG. 33 is a flowchart showing another embodiment of the peak air-fuel ratio detection routine.
- FIG. 34 is a flowchart showing still another embodiment of the peak air-fuel ratio detection routine.
- Fig. 1 shows an overall view of a compression ignition type internal combustion engine.
- 1 is an engine body
- 2 is a combustion chamber of each cylinder
- 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber
- 4 is an intake manifold
- 5 is an exhaust manifold.
- the intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8.
- a throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6.
- a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6.
- the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.
- the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7.
- the outlet of the exhaust turbine 7b is connected to the inlet of the exhaust purification catalyst 13 via the exhaust pipe 12a, and the outlet of the exhaust purification catalyst 13 is used to collect particulates contained in the exhaust gas via the exhaust pipe 12b. It is connected to the particulate filter 14.
- a hydrocarbon supply valve 15 for supplying hydrocarbons composed of light oil and other fuels used as fuel for the compression ignition internal combustion engine is disposed. In the embodiment shown in FIG.
- the hydrocarbon supply valve 15 supplies hydrocarbons made of gasoline or other fuel used as fuel for the spark ignition internal combustion engine.
- the exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 16, and an electronically controlled EGR control valve 17 is disposed in the EGR passage 16.
- EGR exhaust gas recirculation
- a cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed around the EGR passage 16.
- each fuel injection valve 3 is connected to a common rail 20 via a fuel supply pipe 19, and this common rail 20 is connected to a fuel tank 22 via an electronically controlled fuel pump 21 having a variable discharge amount.
- the fuel stored in the fuel tank 22 is supplied into the common rail 20 by the fuel pump 21, and the fuel supplied into the common rail 20 is supplied to the fuel injection valve 3 through each fuel supply pipe 19.
- the electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31.
- An upstream air-fuel ratio sensor 23 for detecting the air-fuel ratio of the exhaust gas discharged from the engine is disposed in the exhaust pipe 12 a upstream of the hydrocarbon supply valve 15, and the exhaust pipe 12 b downstream of the exhaust purification catalyst 13.
- a downstream air-fuel ratio sensor 24 for detecting the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst 13 is disposed inside.
- a temperature sensor 24 for detecting the temperature of the exhaust purification catalyst 13 is disposed downstream of the exhaust purification catalyst 13, and the particulate filter 14 is for detecting a differential pressure before and after the particulate filter 14.
- a differential pressure sensor 26 is attached.
- Output signals of the upstream air-fuel ratio sensor 23, downstream air-fuel ratio sensor 24, temperature sensor 25, differential pressure sensor 26, and intake air amount detector 8 are input to the input port 35 via corresponding AD converters 37, respectively.
- the A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done.
- the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °.
- FIG. 2 schematically shows the surface portion of the catalyst carrier carried on the substrate of the exhaust purification catalyst 13.
- noble metal catalysts 51 and 52 are supported on a catalyst support 50 made of alumina, for example, and further on this catalyst support 50 potassium K, sodium Na, cesium Cs.
- Alkaline metals such as barium Ba, alkaline earth metals such as calcium Ca, rare earths such as lanthanoids and silver Ag, copper Cu, iron Fe, NO such as iridium Ir X
- a basic layer 53 containing at least one selected from metals capable of donating electrons is formed. Since the exhaust gas flows along the catalyst carrier 50, it can be said that the noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13. Further, since the surface of the basic layer 53 exhibits basicity, the surface of the basic layer 53 is referred to as a basic exhaust gas flow surface portion 54.
- the noble metal catalyst 51 is made of platinum Pt
- the noble metal catalyst 52 is made of rhodium Rh.
- the noble metal catalysts 51 and 52 carried on the catalyst carrier 50 are composed of platinum Pt and rhodium Rh.
- palladium Pd can be further supported on the catalyst carrier 50 of the exhaust purification catalyst 13, or palladium Pd can be supported instead of rhodium Rh.
- the noble metal catalysts 51 and 52 supported on the catalyst carrier 50 are composed of platinum Pt and at least one of rhodium Rh and palladium Pd.
- FIG. 3 schematically shows the reforming action performed in the exhaust purification catalyst 13 at this time.
- the hydrocarbon HC injected from the hydrocarbon feed valve 15 is converted into a radical hydrocarbon HC having a small number of carbons by the catalyst 51.
- FIG. 4 shows the supply timing of hydrocarbons from the hydrocarbon supply valve 15 and the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13. Since the change in the air-fuel ratio (A / F) in depends on the change in the concentration of hydrocarbons in the exhaust gas flowing into the exhaust purification catalyst 13, the air-fuel ratio (A / F) in shown in FIG. It can be said that the change represents a change in hydrocarbon concentration.
- FIG. 5 shows a change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 as shown in FIG. 4 by periodically changing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13. NO by the exhaust purification catalyst 13 when X The purification rate is shown for each catalyst temperature TC of the exhaust purification catalyst 13. The inventor has NO over a long period of time.
- FIG. 6A and 6B In the research course, when the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is vibrated with an amplitude within a predetermined range and a period within a predetermined range, FIG. As shown in Fig. 4, extremely high NO even in a high temperature region of 400 ° C or higher. X It has been found that a purification rate can be obtained. Further, at this time, a large amount of the reducing intermediate containing nitrogen and hydrocarbon continues to be held or adsorbed on the surface of the basic layer 53, that is, on the basic exhaust gas flow surface portion 54 of the exhaust purification catalyst 13. Reducing intermediate is high NO X It turns out that it plays a central role in obtaining the purification rate. Next, this will be described with reference to FIGS. 6A and 6B.
- FIGS. 6A and 6B schematically show the surface portion of the catalyst carrier 50 of the exhaust purification catalyst 13, and in these FIGS. 6A and 6B, the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is predetermined.
- the reaction is shown to be presumed to occur when oscillated with an amplitude within a range and a period within a predetermined range.
- FIG. 6A shows a case where the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is low
- FIG. 6B shows that the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 when hydrocarbons are supplied from the hydrocarbon supply valve 15 is high. It shows when As can be seen from FIG.
- This reducing intermediate is attached or adsorbed on the surface of the basic layer 53.
- the first reducing intermediate produced at this time is the nitro compound R-NO. 2 It is thought that.
- This nitro compound R-NO 2 Is produced, it becomes a nitrile compound R-CN, but this nitrile compound R-CN can only survive for a moment in that state, so it immediately becomes an isocyanate compound R-NCO.
- this isocyanate compound R-NCO is hydrolyzed, the amine compound R-NH 2 It becomes. However, in this case, it is considered that a part of the isocyanate compound R-NCO is hydrolyzed. Therefore, as shown in FIG.
- Active NO at this time X * Is a reducing intermediate R-NCO or R-NH 2 Reacts with N 2 , CO 2 , H 2 O, so NO X Will be purified.
- a reducing intermediate is generated by increasing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13, and the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is decreased to reduce the oxygen concentration.
- the exhaust purification catalyst 13 makes NO. X In order to purify, it is necessary to periodically change the concentration of hydrocarbons flowing into the exhaust purification catalyst 13.
- the produced reducing intermediate is activated NO.
- X * It is necessary to reduce the hydrocarbon concentration to a concentration low enough to react with. That is, it is necessary to vibrate the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 with an amplitude within a predetermined range.
- the generated reducing intermediate is active NO.
- X * Sufficient amounts of reducing intermediates R-NCO and R-NH until 2 Must be retained on the basic layer 53, that is, on the basic exhaust gas flow surface portion 54.
- a basic exhaust gas flow surface portion 54 is provided.
- noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13, and the generated reducing intermediates R-NCO and R-NH 2 Is maintained around the noble metal catalyst 51, 52, a basic exhaust gas flow surface portion 54 is formed around the noble metal catalyst 51, 52, and is held on the basic exhaust gas flow surface portion 54.
- the injection interval is 3 seconds.
- the oscillation period of hydrocarbon concentration that is, the supply period of hydrocarbon HC is longer than the period within the above-mentioned predetermined range
- the reducing intermediates R-NCO and R-NH are formed on the surface of the basic layer 53. 2 Disappears, and at this time, the active NO produced on platinum Pt53 X * Is nitrate ion NO as shown in FIG. 7A. 3 ⁇ In the form of nitrate in the form of nitrate. That is, at this time, NO in the exhaust gas X Will be absorbed in the basic layer 53 in the form of nitrate.
- FIG. 1 In the form of nitrate in the form of nitrate. That is, at this time, NO in the exhaust gas X Will be absorbed in the basic layer 53 in the form of nitrate.
- X NO for temporary storage X It plays the role of a storage agent. That is, in this case, if the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the exhaust purification catalyst 13 is referred to as the air-fuel ratio of the exhaust gas, the exhaust purification catalyst. 13 is NO when the air-fuel ratio of the exhaust gas is lean X NO is stored when the oxygen concentration in the exhaust gas decreases. X NO release X It functions as a storage catalyst. FIG. 9 shows that the exhaust purification catalyst 13 is NO in this way.
- the purification rate is shown.
- the horizontal axis in FIG. 9 indicates the catalyst temperature TC of the exhaust purification catalyst 13.
- Set the exhaust purification catalyst 13 to NO X When functioning as an occlusion catalyst, as shown in FIG. 9, when the catalyst temperature TC is 300 ° C. to 400 ° C., extremely high NO X A purification rate can be obtained, but NO when the catalyst temperature TC reaches 400 ° C or higher.
- X The purification rate decreases. ⁇ If the catalyst temperature TC reaches 400 ° C or higher, NO X The purification rate decreases because when the catalyst temperature TC reaches 400 ° C. or higher, the nitrate is thermally decomposed and NO.
- the hydrocarbon supply valve 15 for supplying hydrocarbons is disposed in the engine exhaust passage, and the NO contained in the exhaust gas in the engine exhaust passage downstream of the hydrocarbon supply valve 15 is provided.
- An exhaust purification catalyst 13 for reacting with the reformed hydrocarbon is disposed, and noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13 and around the noble metal catalysts 51 and 52 Is formed with a basic exhaust gas flow surface portion 54, and the exhaust purification catalyst 13 sets the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 within a predetermined range and an amplitude within a predetermined range. If it is vibrated with the period of NO, NO contained in the exhaust gas X NO and contained in the exhaust gas when the oscillation period of the hydrocarbon concentration is longer than this predetermined range.
- the purification method carries a noble metal catalyst and NO. X
- NO hardly forms nitrates.
- X New NO to purify X It can be said that it is a purification method. In fact, this new NO X When the purification method is used, the exhaust purification catalyst 13 is set to NO.
- FIG. 10 shows an enlarged view of the change in the air-fuel ratio (A / F) in shown in FIG.
- the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 indicates the change in the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 at the same time.
- ⁇ H indicates the amplitude of the change in the concentration of hydrocarbon HC flowing into the exhaust purification catalyst 13, and ⁇ T indicates the oscillation period of the concentration of hydrocarbon flowing into the exhaust purification catalyst 13.
- (A / F) b represents the base air-fuel ratio indicating the air-fuel ratio of the combustion gas for generating the engine output.
- the base air-fuel ratio (A / F) b represents the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 when the supply of hydrocarbons is stopped.
- X represents the generated active NO.
- X * Represents the upper limit of the air-fuel ratio (A / F) in used for the production of the reducing intermediate without being occluded in the basic layer 53 in the form of nitrate, X * It is necessary to make the air-fuel ratio (A / F) in lower than the upper limit X of this air-fuel ratio in order to cause the reduced hydrocarbon to react with the reformed hydrocarbon.
- X in Fig. 10 is active NO X * Represents the lower limit of the hydrocarbon concentration required to produce a reducing intermediate by reacting the modified hydrocarbon with the modified hydrocarbon. It is necessary to make it higher than the lower limit X. In this case, whether or not a reducing intermediate is generated depends on the active NO.
- the ratio between the surrounding oxygen concentration and the hydrocarbon concentration, that is, the air-fuel ratio (A / F) in, is determined by the above-mentioned upper limit X of the air-fuel ratio necessary for generating the reducing intermediate, Called.
- the required minimum air-fuel ratio X is rich. Therefore, in this case, the air-fuel ratio (A / F) in is instantaneously required to generate the reducing intermediate. The following is made rich:
- the required minimum air-fuel ratio X is lean.
- the reducing intermediate is generated by periodically reducing the air-fuel ratio (A / F) in while maintaining the air-fuel ratio (A / F) in lean.
- the required minimum air-fuel ratio X becomes rich or lean depends on the oxidizing power of the exhaust purification catalyst 13.
- the exhaust purification catalyst 13 becomes stronger in oxidizing power, and if it becomes more acidic, the oxidizing power becomes stronger. Accordingly, the oxidizing power of the exhaust purification catalyst 13 varies depending on the amount of the precious metal 51 supported and the acidity.
- the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG.
- the exhaust purification catalyst 13 having a weak oxidizing power when used, the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG. As a result, some of the hydrocarbons are not completely oxidized but are partially oxidized, that is, the hydrocarbons are reformed, thus producing a reducing intermediate.
- the exhaust purification catalyst 13 having a weak oxidizing power if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, a large amount of hydrocarbons are not oxidized. The exhaust gas is simply exhausted from the exhaust purification catalyst 13, and the amount of hydrocarbons that are wasted is increased.
- the required minimum air-fuel ratio X needs to be made lean. That is, it can be seen that the required minimum air-fuel ratio X needs to be lowered as the oxidizing power of the exhaust purification catalyst 13 becomes stronger, as shown in FIG. As described above, the required minimum air-fuel ratio X becomes lean or rich due to the oxidizing power of the exhaust purification catalyst 13, but the case where the required minimum air-fuel ratio X is rich will be described as an example. The amplitude of the change in the concentration of the inflowing hydrocarbon and the oscillation period of the concentration of the hydrocarbon flowing into the exhaust purification catalyst 13 will be described.
- the air-fuel ratio (A / F) in is made equal to or less than the required minimum air-fuel ratio X.
- NO X As described above, it is necessary to oxidize the surplus hydrocarbons in order to purify the water well. X In order to purify the water well, a larger amount of excess hydrocarbon requires more oxygen. In this case, the amount of oxygen can be increased by increasing the oxygen concentration in the exhaust gas.
- NO X In order to purify the gas well, it is necessary to increase the oxygen concentration in the exhaust gas after the hydrocarbon is supplied when the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is high. That is, it is necessary to increase the amplitude of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher.
- Figure 13 shows the same NO X It shows the relationship between the oxygen concentration in the exhaust gas before the hydrocarbon is supplied and the amplitude ⁇ H of the hydrocarbon concentration when the purification rate is obtained. The same NO from FIG. X It can be seen that in order to obtain the purification rate, it is necessary to increase the amplitude ⁇ H of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher.
- the same NO X In order to obtain the purification rate, it is necessary to increase the amplitude ⁇ T of the hydrocarbon concentration as the base air-fuel ratio (A / F) b increases. In other words, NO X In order to purify the gas well, the amplitude ⁇ T of the hydrocarbon concentration can be reduced as the base air-fuel ratio (A / F) b becomes lower.
- the base air-fuel ratio (A / F) b is the lowest during acceleration operation, and if the hydrocarbon concentration amplitude ⁇ H is about 200 ppm, NO X Can be purified well.
- the base air-fuel ratio (A / F) b is usually larger than that during acceleration operation. Therefore, as shown in FIG.
- the predetermined range of the amplitude of the hydrocarbon concentration is set to 200 ppm to 10,000 ppm.
- the vibration period ⁇ T of the hydrocarbon concentration becomes long, after the hydrocarbon is supplied, the active NO is X * The surrounding oxygen concentration becomes high.
- the vibration period ⁇ T of the hydrocarbon concentration when the vibration period ⁇ T of the hydrocarbon concentration is longer than about 5 seconds, the active NO X * Will begin to be absorbed in the basic layer 53 in the form of nitrate, and therefore, as shown in FIG. 15, when the vibration period ⁇ T of the hydrocarbon concentration becomes longer than about 5 seconds, NO X The purification rate will decrease. Therefore, the vibration period ⁇ T of the hydrocarbon concentration needs to be 5 seconds or less.
- the vibration period ⁇ T of the hydrocarbon concentration becomes approximately 0.3 seconds or less, the supplied hydrocarbon starts to accumulate on the exhaust gas flow surface of the exhaust purification catalyst 13, and therefore, as shown in FIG.
- NO X When the vibration period ⁇ T of the motor becomes approximately 0.3 seconds or less, NO X The purification rate decreases.
- the vibration period of the hydrocarbon concentration is set to be between 0.3 seconds and 5 seconds.
- the purification method will be specifically described. In this way, the exhaust purification catalyst 13 is changed to NO. X NO when functioning as a storage catalyst X
- the purification method is hereinafter referred to as the second NO. X This is called a purification method.
- This second NO X In the purification method, the occluded NO occluded in the basic layer 53 as shown in FIG.
- the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 is temporarily made rich.
- the air-fuel ratio (A / F) in of the exhaust gas is made rich, the NO stored in the basic layer 53 when the air-fuel ratio (A / F) in of the exhaust gas is lean X Are released from the basic layer 53 at once and reduced. NO X Is purified. Occlusion NO X
- the amount ⁇ NOX is, for example, NO discharged from the engine X Calculated from the quantity.
- the emission NO discharged from the engine per unit time X The amount NOXA is stored in advance in the ROM 32 as a function of the engine output torque Te and the engine speed N in the form of a map as shown in FIG. X From NOXA to NO X An amount ⁇ NOX is calculated.
- the period during which the air-fuel ratio (A / F) in of the exhaust gas is made rich is usually 1 minute or more.
- This second NO X In the purification method, as shown in FIG.
- the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 by injecting the additional fuel WR in addition to the output generating fuel Q from the fuel injection valve 3 into the combustion chamber 2 ( A / F) in is made rich.
- the horizontal axis in FIG. 18 indicates the crank angle.
- This additional fuel WR is injected when it burns but does not appear as engine output, that is, slightly before ATDC 90 ° after compression top dead center.
- This fuel amount WR is stored in advance in the ROM 32 in the form of a map as shown in FIG. 19 as a function of the engine output torque Te and the engine speed N.
- the air-fuel ratio (A / F) in of the exhaust gas can be made rich by increasing the amount of hydrocarbons supplied from the hydrocarbon supply valve 15 in this case.
- the first NO again X Returning to the explanation of the purification method, the first NO X NO using the purification method X As described above, it is necessary to appropriately control the amplitude ⁇ H and the vibration period ⁇ T of the hydrocarbon concentration.
- the amplitude ⁇ H of the hydrocarbon concentration is controlled so that the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 is equal to or less than the required minimum air-fuel ratio X, It is necessary to control the oscillation period ⁇ T of the concentration between 0.3 seconds and 5 seconds.
- the amplitude ⁇ H of the hydrocarbon concentration is controlled to control the injection amount of hydrocarbons from the hydrocarbon feed valve 15, and the oscillation period ⁇ T of the hydrocarbon concentration is controlled by the hydrocarbons from the hydrocarbon feed valve 15. It is controlled by controlling the injection cycle.
- the injection amount of hydrocarbons from the hydrocarbon supply valve 15 can be controlled by controlling at least one of the injection time or injection pressure of hydrocarbons from the hydrocarbon supply valve 15.
- the embodiment according to the present invention will be described below by taking as an example the case where the injection amount is controlled by controlling the injection time while keeping the injection pressure constant.
- the optimum opening degree of the throttle valve 10 and the optimum opening degree of the EGR control valve 17 corresponding to the operating state of the engine are obtained in advance by experiments, and the throttle valve 10 and the EGR control are further determined.
- the optimum base air-fuel ratio (A / F) b obtained when the valve 17 is set to the optimum opening degree is also obtained in advance by experiments.
- the fuel injection amount from the fuel injection valve 3 is controlled so that the air-fuel ratio of the exhaust gas discharged from the engine becomes this optimal base air-fuel ratio (A / F) b.
- the first NO X NO by purification method X The highest NO when the purification action is performed X
- An optimum hydrocarbon injection period ⁇ T and an optimum hydrocarbon injection time WT that can obtain a purification rate are obtained in advance by experiments.
- This optimum hydrocarbon injection cycle ⁇ T is stored in advance in the ROM 32 in the form of a map as shown in FIG. 20A as a function of the engine speed N and the engine output torque Te, and this optimum hydrocarbon injection time.
- the WT is also stored in advance in the ROM 32 in the form of a map as shown in FIG. 20B as a function of the engine speed N and the engine output torque Te.
- the hydrocarbon injection cycle is set to the optimal hydrocarbon injection cycle ⁇ T shown in FIG. 20A
- the hydrocarbon injection time is set to the optimal hydrocarbon injection time WT shown in FIG. 20B.
- FIG. 21B shows a change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 at this time, showing a change in the air-fuel ratio (A / F) in of the inflowing exhaust gas.
- the rich-side peak air-fuel ratio (A / F) r of the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 is rich
- the rich-side peak air-fuel ratio (A / F) p of the air-fuel ratio detected by the downstream-side air-fuel ratio sensor 24 is lean. This is because part of the supplied hydrocarbons once adheres to the exhaust purification catalyst 13 and then evaporates with a time difference, thereby smoothing the change in the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst 13. This is considered to be because the peak value of becomes smaller.
- the sensor unit 60 of the air-fuel ratio sensors 23, 24 includes a thin cup-shaped solid electrolyte 61 made of zirconia Zr, a platinum thin film electrode 62 covering the inner peripheral surface of the solid electrolyte 61, and the solid electrolyte 61.
- a platinum thin film electrode 63 covering the outer peripheral surface and a diffusion resistance layer 64 made of alumina covering the periphery of the electrode 63 are configured.
- the sensor unit 60 is covered with a protective cover 66 having a large number of holes 65.
- the sensor unit 60 is disposed in the exhaust gas, and the exhaust gas is guided to the diffusion resistance layer 64 through the hole 65.
- a constant voltage E is applied between the electrodes 62 and 63.
- a current I as shown in FIG. 22B is applied between the electrodes 62 and 63 according to the air-fuel ratio of the exhaust gas. Flows.
- the air-fuel ratio is obtained from the current value I based on the relationship shown in FIG. 22B. That is, the air-fuel ratio is detected from the outputs of the air-fuel ratio sensors 23 and 24.
- the air-fuel ratio sensors 23 and 24 X It is thought that it is influenced by.
- the air-fuel ratio detected by the air-fuel ratio sensors 23, 24 is the SO contained in the exhaust gas. X So far, it has not been known at all how it is affected. Therefore, the present inventor has found that the air-fuel ratio detected by the air-fuel ratio sensors 23, 24 is SO. X As a result, the relationship between the air-fuel ratio detected by the air-fuel ratio sensors 23 and 24 and the sulfur poisoning of the air-fuel ratio sensors 23 and 24 was found. Next, this will be described by taking the downstream side air-fuel ratio sensor 24 as an example. The solid line in FIG.
- FIG. 23A shows the change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 shown in FIG. 21A as it is. That is, the solid line in FIG. 23A shows the change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 when the downstream air-fuel ratio sensor 24 is not sulfur poisoning.
- a sulfur component adheres to the downstream air-fuel ratio sensor 24, as the amount of sulfur component attached to the downstream air-fuel ratio sensor 24 increases, it is detected by the downstream air-fuel ratio sensor 24 as shown by a broken line in FIG. 23A. It has been found that the change amount of the air-fuel ratio becomes smaller and the change period of the air-fuel ratio becomes longer. The reason is considered as follows. That is, in the air-fuel ratio sensor shown in FIG.
- oxygen and hydrocarbons contained in the exhaust gas diffuse in the diffusion resistance layer 64 to reach the electrode 63, and the hydrocarbon is oxidized on the electrode 63.
- oxygen is excessive, oxygen ions move in the solid electrolyte 61 from the electrodes 63 to 62. If oxygen is insufficient, oxygen ions move in the solid electrolyte 61 from the electrodes 62 to 63.
- the air-fuel ratio is detected by the current I generated by the movement.
- SO is in the exhaust gas. X If this is included, this SO X also penetrates into the diffusion resistance layer 64, reacts with platinum on the electrode 63 on the one hand to form PtS, and on the other hand, forms SOt in the diffusion resistance layer 64.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 can be detected from the change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24.
- the upstream air-fuel ratio sensor 23 the upstream air-fuel ratio sensor 23.
- the air-fuel ratio sensors 23, 24 have the solid electrolyte 61, the electrodes 62, 63 that cover both side surfaces of the solid electrolyte 61, and the diffusion resistance layer 64 that covers one electrode 63, and the exhaust gas is
- the air-fuel ratio of the exhaust gas changes and the air-fuel ratio detected by the air-fuel ratio sensors 23, 24 changes, it is detected by the air-fuel ratio sensors 23, 24.
- the change in the air-fuel ratio depends on the amount of sulfur component attached to the air-fuel ratio sensors 23, 24. At this time, the larger the amount of sulfur component attached to the air-fuel ratio sensors 23, 24, the more the air-fuel ratio sensors 23, 24 detect. The change amount of the air-fuel ratio becomes smaller and the change period of the air-fuel ratio becomes longer.
- FIG. 23B shows the relationship between the reduction rate ⁇ AFR of the rich-side peak air-fuel ratio of the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 and the sulfur poisoning amount.
- This peak air-fuel ratio decrease rate ⁇ AFR is expressed by the following equation.
- ⁇ AFR ( ⁇ AFp ⁇ AFz) / ⁇ AFp
- ⁇ AFp (A / F) b ⁇ (A / F)
- p ⁇ AFz (A / F) b ⁇ (A / F) z
- the base air-fuel ratio (A / F) b is determined in accordance with the operating state of the engine.
- the rich-side peak air-fuel ratio (A / F) p detected by the downstream-side air-fuel ratio sensor 24 when the downstream-side air-fuel ratio sensor 24 does not cause sulfur poisoning has been obtained in advance by experiments.
- the rich-side peak air-fuel ratio (A / F) p obtained by the above is stored in advance in the ROM 32 in the form of a map as shown in FIG. 24 as a function of the engine speed N and the engine output torque Te. Therefore, ⁇ AFp is determined in accordance with the operation state of the engine.
- the rich-side peak air-fuel ratio (A / F) z is a value detected by the downstream-side air-fuel ratio sensor 24. From the detected rich-side peak air-fuel ratio (A / F) z and the engine operating state, ⁇ AFz is calculated from the determined base air-fuel ratio (A / F) b.
- the peak air-fuel ratio decrease rate ⁇ AFR is calculated from the rich-side peak air-fuel ratio (A / F) z detected by the downstream air-fuel ratio sensor 24.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 increases as the peak air-fuel ratio decrease rate ⁇ AFR increases.
- the rich peak air-fuel ratio (A / F) z detected by the downstream air-fuel ratio sensor 24 also increases when the hydrocarbon feed valve 15 is clogged and the hydrocarbon feed rate decreases. As a result, the peak air-fuel ratio decrease rate ⁇ AFR increases.
- the hydrocarbon feed valve 15 is clogged relatively rapidly, and once clogged, it does not change so much as shown by the broken line in FIG. 25. Therefore, the temporal change in the peak air-fuel ratio reduction rate ⁇ AFR is monitored. If the operation continues, it can be determined whether the peak air-fuel ratio decrease rate ⁇ AFR has increased due to sulfur poisoning of the downstream air-fuel ratio sensor 24 or whether the peak air-fuel ratio decrease rate ⁇ AFR has increased due to clogging of the hydrocarbon feed valve 15. become.
- the downstream air-fuel ratio sensor 24 has been poisoned by sulfur from the temporal change of the peak air-fuel ratio decrease rate ⁇ AFR, that is, from the change of the air-fuel ratio detected by the downstream air-fuel ratio sensor 24. Or whether the hydrocarbon supply valve 15 is clogged.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 is obtained from the integrated value of the difference between the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 and the base air-fuel ratio (A / F) b. .
- the downstream air-fuel ratio sensor 24 is not poisoned with sulfur.
- the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 is instantaneously completed within a predetermined period shown by A in FIG. 26A.
- the downstream air-fuel ratio sensor 24 is sulfur poisoned, the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 is a predetermined period A as shown by the broken line in FIG. Continue to change beyond.
- the downstream air-fuel ratio sensor 24 is not sulfur-poisoned, when the hydrocarbon is injected once from the hydrocarbon supply valve 15, the downstream air-fuel ratio sensor 24.
- the area SA is large but the area SB is almost zero, whereas this is indicated by the broken line.
- the downstream air-fuel ratio sensor 24 is sulfur poisoned, the area SA becomes smaller and the area SB becomes larger. That is, it can be seen that the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 appears significantly in the ratio of the area SB to the area SA.
- 26B shows the relationship between the ratio SB / SA of the area SB to the area SA and the sulfur poisoning amount, and it can be seen that the sulfur poisoning amount increases as the ratio SB / SA increases. Therefore, in the embodiment according to the present invention, the integral values SA and SB of the difference between the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 and the base air-fuel ratio (A / F) b are calculated, and the air-fuel ratio of the exhaust gas is calculated. The air-fuel ratio detected by the downstream air-fuel ratio sensor 24 changes instantaneously within a predetermined period A unless the downstream air-fuel ratio sensor 24 is sulfur-poisoned.
- the amount of sulfur poisoning in the downstream air-fuel ratio sensor 24 increases, it continues to change beyond the predetermined period A, and exceeds the integral value SA and the predetermined period A within the predetermined period A.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 is detected from the ratio SB / SA with the integrated value SB at the time.
- the value of the integral value SA an average value during which the air-fuel ratio varies a plurality of times can be used
- an average value during which the air-fuel ratio varies a plurality of times can be used.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 can be obtained from the rich-side peak air-fuel ratio (A / F) z detected by the downstream air-fuel ratio sensor 24, or the downstream air-fuel ratio sensor 24. It can also be obtained from the ratio SB / SA of the integral values SA and SB of the difference between the air-fuel ratio detected by the above and the base air-fuel ratio (A / F) b. Therefore, when these are comprehensively expressed, a value representative of a change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 when no sulfur poisoning occurs is obtained in advance as the reference value.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 is detected from a value representative of the change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24.
- the value representative of the change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 is the rich peak air-fuel ratio (A / F) z
- the reference value is 24 is a rich peak air-fuel ratio (A / F) p stored in advance.
- the value representative of the change in the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 exceeds the integral value SA within the predetermined period A and the predetermined period A.
- the ratio SB / SA with the integrated value SB at this time, and the reference value in this case is almost zero (SB / SA ⁇ 0).
- these reference values can be obtained in advance or can be actually measured.
- the sulfur poisoning recovery process is performed before the reference value is actually measured. It is necessary to keep it.
- FIG. 27 taking as an example the case where the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 is obtained from the rich-side peak air-fuel ratio (A / F) z.
- the sulfur-poisoning recovery process of the downstream air-fuel ratio sensor 24 is performed.
- the SO adhering to the downstream air-fuel ratio sensor 24 X Indicates that the temperature of the downstream air-fuel ratio sensor 24 is about 650 ° C.
- the SO is released from the downstream air-fuel ratio sensor 24 and adheres to the downstream air-fuel ratio sensor 24.
- X Indicates that the air-fuel ratio of the exhaust gas flowing into the downstream air-fuel ratio sensor 24 is rich and the temperature of the downstream air-fuel ratio sensor 24 is about 500 ° C.
- the downstream air-fuel ratio sensor 24 detects SO.
- X Is to be released that is, when sulfur poisoning of the downstream air-fuel ratio sensor 24 is to be recovered, the temperature of the downstream air-fuel ratio sensor 24 is about 650 ° C.
- the SO 2 is raised to the decomposition temperature or the temperature of the downstream air-fuel ratio sensor 24 is about 500 ° C.
- the air-fuel ratio of the exhaust gas raised to the discharge temperature and flowing into the downstream air-fuel ratio sensor 24 is made rich. As shown in FIG.
- the rich-side peak air-fuel ratio (reference value) becomes the reference value based on the air-fuel ratio detected by the downstream air-fuel ratio sensor 24.
- a / F) p is detected. Note that the rich side peak air-fuel ratio (A / F) p changes the temperature of the downstream side air-fuel ratio sensor 24, that is, the temperature of the exhaust gas, even if the amount of supplied hydrocarbon is the same, and the flow rate of the exhaust gas changes. Then it changes with it.
- the rich-side peak air-fuel ratio is when the temperature of the exhaust gas is within the predetermined temperature range and the flow rate of the exhaust gas, that is, the intake air amount is within the predetermined flow rate range.
- a / F is a detection condition for detecting p, and a rich-side peak that becomes a reference value based on the air-fuel ratio detected by the downstream air-fuel ratio sensor 24 when this detection condition is satisfied.
- An air-fuel ratio (A / F) p is detected. As shown in FIG. 27, when the rich-side peak air-fuel ratio (A / F) p serving as the reference value is detected, it is detected by the downstream-side air-fuel ratio sensor 24 every time this detection condition is satisfied thereafter.
- the rich-side peak air-fuel ratio (A / F) z is detected from the air-fuel ratio, and the peak air-fuel ratio reduction rate ⁇ AFR is calculated from these rich-side peak air-fuel ratios (A / F) p and (A / F) z.
- the peak air-fuel ratio reduction rate ⁇ AFR changes rapidly as shown by the broken line in FIG. The interval at which the rate ⁇ AFR reaches the allowable value RX becomes shorter. Therefore, it can be detected from this that the fuel having a high sulfur concentration has been used.
- the hydrocarbon supply is performed.
- the supply amount of hydrocarbons from the valve 15 is increased compared to the supply amount of hydrocarbons determined from the operating state of the engine.
- the rich side peak air-fuel ratio of the air-fuel ratio of the exhaust gas is further set to the rich side.
- SO in the exhaust gas 2 If this is included, this SO 2 Is oxidized on platinum Pt53 and SO 3 It becomes. Then this SO 3 Is stored in the basic layer 53 and sulfate ions SO. 4 2- To form a stable sulfate salt. However, this sulfate is stable and difficult to decompose, and if the air-fuel ratio of the exhaust gas is simply made rich, the sulfate remains as it is without being decomposed. In this case, NO increases when the stored amount of stored sulfate increases. X The purification rate decreases.
- the temperature of the exhaust purification catalyst 13 is about 650 ° C.
- the SO stored from the exhaust purification catalyst 13 is increased.
- the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 is alternately changed as shown in FIG. 29 by controlling the additional fuel amount WR into the combustion chamber 2. Switching between rich and lean, so that the temperature of the exhaust purification catalyst 13 is about 500 ° C. SO X
- the SO stored in the exhaust purification catalyst 13 is increased to the discharge temperature and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 is intermittently made rich. X To be released.
- the sulfur poisoning amount of the downstream air-fuel ratio sensor 24 is calculated based on the air-fuel ratio detected by the downstream air-fuel ratio sensor 24.
- the SO to the downstream air-fuel ratio sensor 24 is X If the amount of adhesion increases, the SO to the exhaust purification catalyst 13 X The amount of occlusion increases. That is, the sulfur poisoning amount of the exhaust purification catalyst 13 can be estimated from the sulfur poisoning amount of the air-fuel ratio sensor. Therefore, in the embodiment according to the present invention, the sulfur poisoning amount of the exhaust purification catalyst 13 is estimated from the change in the air-fuel ratio detected by the air-fuel ratio sensor. More specifically, in the embodiment according to the present invention, the sulfur poisoning amount of the exhaust purification catalyst 13 is estimated from the sulfur poisoning amount of the downstream air-fuel ratio sensor 24.
- step 71 the discharge NO per unit time is determined from the map shown in FIG. X The quantity NOXA is calculated.
- NO is discharged to ⁇ NOX.
- An amount ⁇ NOX is calculated.
- step 73 NO is stored. X It is determined whether or not the amount ⁇ NOX exceeds the allowable value MAX. When it is determined in step 73 that ⁇ NOX ⁇ MAX, the routine proceeds to step 74 where fuel injection processing from the fuel injection valve 3 is performed.
- step 73 fuel is injected from the fuel injection valve 3 so as to obtain a predetermined lean air-fuel ratio determined from the operating state of the engine.
- step 73 determines whether fuel is injected from the fuel injection valve 3 so as to obtain a predetermined lean air-fuel ratio determined from the operating state of the engine.
- step 75 rich control I is performed. That is, the additional fuel amount WR is calculated from the map shown in FIG. 19, and the additional fuel injection action is performed.
- step 76 ⁇ NOX is cleared.
- step 70 when it is determined at step 70 that TC ⁇ TCo, that is, when the exhaust purification catalyst 13 is activated, the routine proceeds to step 77, where it is determined whether TC ⁇ TCo at the previous interruption.
- the routine proceeds to step 78 where the rich control II is executed.
- the additional fuel amount WR is calculated from the map shown in FIG. 19, and the additional fuel injection action is performed and the NO stored in the exhaust purification catalyst 13. X Is released.
- step 79 ⁇ NOX is cleared.
- step 80 the routine proceeds to step 80, where the first NO according to the present invention is determined.
- X NO by purification method X Purifying action is performed. That is, when the exhaust purification catalyst 13 is not activated, the second NO X NO by purification method X When the purification action is performed and the exhaust purification catalyst 13 is activated, the second NO X NO from the purification method X Switch to purification method. Second NO X NO from the purification method X When switched to the purification method, NO is given to the exhaust purification catalyst 13 X Is stored, the NO stored in the exhaust purification catalyst 13 X Is released at once without being reduced.
- the NO stored in the exhaust purification catalyst 13 in this way.
- X In order to prevent the NO from being released at once without being reduced, the second NO X NO from the purification method X Immediately before switching to the purification method, the second NO in step 78. X Occluded NO from the exhaust purification catalyst 13 by the purification method X Rich control II is performed to release the. Now, referring to FIG. 31, first, at step 80, it is judged if the particulate filter 14 is being regenerated.
- the routine proceeds to step 81, where it is judged from the output signal of the differential pressure sensor 26 whether or not the differential pressure ⁇ P before and after the particulate filter 14 has exceeded a predetermined limit value PX.
- ⁇ P ⁇ PX the routine proceeds to step 83 where the SO stored from the exhaust purification catalyst 13 is stored.
- X Is determined, that is, whether or not the sulfur poisoning recovery process of the exhaust purification catalyst 13 is being performed.
- step 84 the peak air-fuel ratio decrease rate ⁇ AFR is calculated, and it is determined whether or not the calculated peak air-fuel ratio decrease rate ⁇ AFR exceeds the allowable value RX.
- the routine proceeds to step 86.
- steps 86 and 87 based on the output signal of the upstream air-fuel ratio sensor 23, the amount of fuel supplied to the engine combustion chamber 2 so that the air-fuel ratio of the exhaust gas discharged from the engine becomes a predetermined air-fuel ratio.
- the hydrocarbon feed valve 15 is controlled such that the amplitude of the change in the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 becomes an amplitude within a predetermined range based on the output signal of the downstream air-fuel ratio sensor 24.
- the injection amount of hydrocarbons from is controlled. Specifically, in step 86, the air-fuel ratio of the exhaust gas discharged from the engine based on the output signal of the upstream air-fuel ratio sensor 23 is the optimum base air-fuel ratio (A / F) according to the operating state of the engine.
- the fuel injection amount from the fuel injection valve 3 is controlled so as to be b.
- the first NO is obtained by feedback control based on the output signal of the downstream air-fuel ratio sensor 24.
- X NO by purification method X Purifying action is performed. That is, the downstream air-fuel ratio sensor 24 detects when the hydrocarbon injection cycle is the optimal hydrocarbon injection cycle ⁇ T shown in FIG. 20A and the hydrocarbon injection time is the optimal hydrocarbon injection time WT shown in FIG. 20B.
- the rich-side peak air-fuel ratio is stored in advance as the target peak air-fuel ratio, and in step 87, the hydrocarbon feed valve is set so that the rich-side peak air-fuel ratio detected by the downstream-side air-fuel ratio sensor 24 becomes the target peak air-fuel ratio.
- the injection time of hydrocarbons from 15 is feedback controlled.
- step 81 when it is determined at step 81 that ⁇ P> PX, the routine proceeds to step 83 where the regeneration process of the particulate filter 14 is performed. The processing cycle is then completed.
- step 84 the routine proceeds to step 85 where the SO stored from the exhaust purification catalyst 13 is stored. X Is released, that is, a process for recovering sulfur poisoning of the exhaust purification catalyst 13 is performed. At the same time, the sulfur poisoning of the downstream air-fuel ratio sensor 24 is also recovered.
- the peak air-fuel ratio reduction rate ⁇ AFR is calculated based on a reference value, and this reference value can be obtained in advance or can be measured.
- the temperature of the downstream air-fuel ratio sensor 24 is about 650 ° C.
- the SO 2 is raised to the decomposition temperature or the temperature of the downstream air-fuel ratio sensor 24 is about 500 ° C.
- the air-fuel ratio of the exhaust gas raised to the discharge temperature and flowing into the downstream air-fuel ratio sensor 24 is made rich.
- the sulfur poisoning of the downstream air-fuel ratio sensor 24 is also recovered. Therefore, in the first example, after the sulfur poisoning recovery process of the exhaust purification catalyst 13 is completed, the rich side peak air-fuel ratio (A) is detected from the air-fuel ratio detected by the downstream side air-fuel ratio sensor 24 when the detection condition is satisfied. / F) p is detected.
- the detection condition is satisfied when the temperature of the exhaust gas is within a predetermined temperature range and the flow rate of the exhaust gas, that is, the intake air amount is within the predetermined flow rate range. It is judged.
- step 100 it is determined whether or not the sulfur poisoning recovery process of the exhaust purification catalyst 13 is being performed.
- the processing cycle is completed. To do.
- the routine proceeds to step 101 where it is judged if the detection condition is satisfied. At this time, if the detection condition is not satisfied, the processing cycle is completed.
- step 102 it is determined whether or not the detection of the rich side peak air-fuel ratio (A / F) p as a reference is completed by the downstream side air-fuel ratio sensor 24.
- step 103 it is determined whether or not a certain time has passed since the sulfur poisoning recovery processing of the exhaust purification catalyst 13 was completed. Is done.
- the routine proceeds to step 104 where the downstream side air-fuel ratio sensor 24 sets the rich-side peak air-fuel ratio (A / F) p as a reference. Detected. That is, it is considered that the downstream air-fuel ratio sensor 24 is not sulfur poisoned when a certain time has not elapsed since the sulfur poisoning recovery processing of the exhaust purification catalyst 13 was completed. Accordingly, when the detection condition is satisfied when a predetermined time has not elapsed since the sulfur poisoning recovery process of the exhaust purification catalyst 13 is completed, the reference rich-side peak air-fuel ratio (A / F) p is detected. Is done.
- step 102 when it is determined in step 102 that the detection of the rich-side peak air-fuel ratio (A / F) p as a reference has been completed, or in step 103, after the sulfur poisoning recovery process of the exhaust purification catalyst 13 is completed, it is constant.
- the routine proceeds to step 105, where the rich-side peak air-fuel ratio (A / F) z is detected from the air-fuel ratio detected by the downstream air-fuel ratio sensor 24. That is, every time the detection condition is satisfied, the rich side peak air-fuel ratio (A / F) z is detected.
- the peak air-fuel ratio decrease rate ⁇ AFR is calculated in step 84 of FIG.
- FIG. 33 shows a routine for detecting the rich-side peak air-fuel ratio (A / F) p and (A / F) z for executing this second example, and this routine is also executed by interruption every predetermined time. Is done.
- step 110 it is first determined in step 110 whether or not the particulate filter 14 is being regenerated. When the particulate filter 14 is being regenerated, the processing cycle is completed. On the other hand, when the regeneration process of the particulate filter 14 is not in progress, the routine proceeds to step 111 where it is judged if the detection condition is satisfied. At this time, if the detection condition is not satisfied, the processing cycle is completed.
- step 112 it is determined whether or not the downstream side air-fuel ratio sensor 24 has completed detection of the reference rich-side peak air-fuel ratio (A / F) p.
- the routine proceeds to step 113, where it is determined whether or not a fixed time has elapsed since the regeneration processing of the particulate filter 14 is completed.
- the routine proceeds to step 114 where the downstream side air-fuel ratio sensor 24 detects the rich-side peak air-fuel ratio (A / F) p. .
- the downstream air-fuel ratio sensor 24 has not been poisoned with sulfur when a predetermined time has not elapsed since the regeneration processing of the particulate filter 14 has been completed. Therefore, when the detection condition is satisfied when a predetermined time has not elapsed since the regeneration process of the particulate filter 14 is completed, the reference rich-side peak air-fuel ratio (A / F) p is detected. On the other hand, when it is determined in step 112 that the detection of the rich peak air-fuel ratio (A / F) p serving as a reference has been completed, or a predetermined time has elapsed since the regeneration processing of the particulate filter 14 is completed in step 113.
- the routine proceeds to step 115, where the rich-side peak air-fuel ratio (A / F) z is detected from the air-fuel ratio detected by the downstream air-fuel ratio sensor 24. That is, also in this case, the rich-side peak air-fuel ratio (A / F) z is detected every time the detection condition is satisfied.
- the peak air-fuel ratio reduction rate ⁇ AFR is calculated from the latest rich-side peak air-fuel ratio (A / F) p and the latest rich-side peak air-fuel ratio (A / F) z.
- the second NO X NO by purification method X The purifying action is performed, and at this time, the occluded NO stored in the basic layer 53 X
- the amount ⁇ NOX exceeds a predetermined allowable amount MAX
- rich processing for temporarily enriching the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 is performed.
- the temperature of the downstream air-fuel ratio sensor 24 is about 500 ° C. SO. X
- the air-fuel ratio of the exhaust gas raised to the discharge temperature and flowing into the downstream air-fuel ratio sensor 24 becomes rich.
- FIG. 34 shows a detection routine for the rich-side peak air-fuel ratio (A / F) p and (A / F) z for executing this third example, and this routine is also executed by interruption at regular intervals. Is done. Referring to FIG. 34, first, at step 120, it is determined whether or not rich processing is being performed during engine high load operation.
- step 121 it is determined whether or not the detection condition is satisfied. At this time, if the detection condition is not satisfied, the processing cycle is completed. On the other hand, when the detection condition is satisfied, the routine proceeds to step 122 where it is determined whether or not the downstream side air-fuel ratio sensor 24 has completed the detection of the reference rich-side peak air-fuel ratio (A / F) p. When the detection of the rich side peak air-fuel ratio (A / F) p is not completed, the routine proceeds to step 123, where it is determined whether or not a fixed time has elapsed since the rich process was completed.
- the routine proceeds to step 124 where the downstream side air-fuel ratio sensor 24 detects the rich-side peak air-fuel ratio (A / F) p. That is, it is considered that the downstream air-fuel ratio sensor 24 is not sulfur-poisoned when a predetermined time has not elapsed since the rich processing at the time of engine high load operation has been completed. Accordingly, when the detection condition is satisfied when a predetermined time has not elapsed since the completion of the rich process, the reference rich-side peak air-fuel ratio (A / F) p is detected.
- step 122 when it is determined in step 122 that the detection of the rich side peak air-fuel ratio (A / F) p as a reference has been completed, or in step 123, it is determined that a certain time has elapsed since the completion of the rich process.
- the routine proceeds to step 125, where the rich side peak air-fuel ratio (A / F) z is detected from the air-fuel ratio detected by the downstream side air-fuel ratio sensor 24. That is, also in this case, the rich-side peak air-fuel ratio (A / F) z is detected every time the detection condition is satisfied.
- the peak air-fuel ratio reduction rate ⁇ AFR is calculated from the latest rich-side peak air-fuel ratio (A / F) p and the latest rich-side peak air-fuel ratio (A / F) z.
- an oxidation catalyst for reforming hydrocarbons can be disposed in the engine exhaust passage upstream of the exhaust purification catalyst 13.
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Abstract
Description
ところでこの空燃比センサは、長期間に亘って高温の排気ガス熱に晒されたり或いは排気ガス中のHCによる被毒作用を受けると次第に劣化し、その結果空燃比センサにより検出される空燃比が実際の空燃比を正確に表さなくなることが知られている。ところが排気ガス中にはSOXが含まれており、この場合空燃比センサはこのSOXの影響を受けるものと考えられる。しかしながら、空燃比センサにより検出された空燃比がこの排気ガス中に含まれるSOXによってどのような影響を受けるかについてはこれまで全く知られていない。 The engine exhaust passage, NO X storage catalyst air-fuel ratio of the inflowing exhaust gas when the lean that releases NO X air-fuel ratio of the exhaust gas which is occluded becomes rich for occluding NO X contained in the exhaust gas inflow was placed, NO fuel addition valve disposed in the X storage catalyst in the engine exhaust passage upstream of the air-fuel ratio sensor arranged in the NO X storage catalyst downstream of the engine exhaust passage, NO based on the output signal of the air-fuel ratio sensor An internal combustion engine in which the air-fuel ratio of exhaust gas flowing into the X storage catalyst is feedback controlled to a target air-fuel ratio is known (see, for example, Patent Document 1).
By the way, this air-fuel ratio sensor gradually deteriorates when exposed to high-temperature exhaust gas heat for a long period of time or when it is poisoned by HC in the exhaust gas. As a result, the air-fuel ratio detected by the air-fuel ratio sensor becomes lower. It is known that the actual air-fuel ratio is not accurately represented. However, SO X is contained in the exhaust gas. In this case, the air-fuel ratio sensor is considered to be affected by this SO X. However, it has not been known at all how the air-fuel ratio detected by the air-fuel ratio sensor is affected by SO X contained in the exhaust gas.
本発明の目的は、この見付け出された関係に基づいて空燃比センサの硫黄被毒を検出するようにした内燃機関の排気浄化装置を提供することにある。 Therefore, the present inventor examined how the air-fuel ratio detected by the air-fuel ratio sensor is affected by SO X contained in the exhaust gas, and as a result, the air-fuel ratio detected by the air-fuel ratio sensor and the air-fuel ratio are detected. They found a relationship with the sensor's sulfur poisoning.
An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that detects sulfur poisoning of an air-fuel ratio sensor based on the found relationship.
図2は触媒担体の表面部分を図解的に示す図である。
図3は排気浄化触媒における酸化反応を説明するための図である。
図4は排気浄化触媒への流入排気ガスの空燃比の変化を示す図である。
図5はNOX浄化率を示す図である。
図6Aおよび6Bは排気浄化触媒における酸化還元反応を説明するための図である。
図7Aおよび7Bは排気浄化触媒における酸化還元反応を説明するための図である。
図8は排気浄化触媒への流入排気ガスの空燃比の変化を示す図である。
図9はNOX浄化率を示す図である。
図10は排気浄化触媒への流入排気ガスの空燃比の変化を示すタイムチャートである。
図11は排気浄化触媒への流入排気ガスの空燃比の変化を示すタイムチャートである。
図12は排気浄化触媒の酸化力と要求最小空燃比Xとの関係を示す図である。
図13は同一のNOX浄化率の得られる、排気ガス中の酸素濃度と炭化水素濃度の振幅ΔHとの関係を示す図である。
図14は炭化水素濃度の振幅ΔHとNOX浄化率との関係を示す図である。
図15は炭化水素濃度の振動周期ΔTとNOX浄化率との関係を示す図である。
図16は排気浄化触媒への流入排気ガスの空燃比の変化等を示す図である。
図17は排出NOX量NOXAのマップを示す図である。
図18は燃料噴射時期を示す図である。
図19は追加の燃料量WRのマップを示す図である。
図20Aおよび20Bは炭化水素の噴射周期等を示す図である。
図21Aおよび21Bは排気浄化触媒への流入排気ガスの空燃比の変化を示すタイムチャートである。
図22Aおよび22Bは図解的に示された空燃比センサの構造等を示す図である。
図23Aおよび23Bは下流側空燃比センサにより検出された空燃比の変化等を示す図である。
図24はピーク空燃比のマップを示す図である。
図25はピーク空燃比低下率の変化を示すタイムチャートである。
図26Aおよび26Bは下流側空燃比センサにより検出された空燃比の変化等を示す図である。
図27はピーク空燃比低下率等の変化を示すタイムチャートである。
図28は排気浄化触媒への流入排気ガスの空燃比の変化等を示す図である。
図29は排気浄化触媒への流入排気ガスの空燃比の変化を示す図である。
図30および31は運転制御を行うためのフローチャートである。
図32はピーク空燃比検出ルーチンの一実施例を示すフローチャートである。
図33はピーク空燃比検出ルーチンの別の実施例を示すフローチャートである。
図34はピーク空燃比検出ルーチンの更に別の実施例を示すフローチャートである。 FIG. 1 is an overall view of a compression ignition type internal combustion engine.
FIG. 2 is a view schematically showing the surface portion of the catalyst carrier.
FIG. 3 is a view for explaining an oxidation reaction in the exhaust purification catalyst.
FIG. 4 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
Figure 5 is a diagram illustrating a NO X purification rate.
6A and 6B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
7A and 7B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
FIG. 8 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
Figure 9 is a diagram illustrating a NO X purification rate.
FIG. 10 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 11 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 12 is a diagram showing the relationship between the oxidizing power of the exhaust purification catalyst and the required minimum air-fuel ratio X.
FIG. 13 is a graph showing the relationship between the oxygen concentration in the exhaust gas and the amplitude ΔH of the hydrocarbon concentration, where the same NO x purification rate can be obtained.
Figure 14 is a diagram showing a relationship between an amplitude ΔH and NO X purification rate of hydrocarbon concentration.
Figure 15 is a diagram showing the relationship between the vibration period ΔT and NO X purification rate of hydrocarbon concentration.
FIG. 16 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
Figure 17 is a diagram illustrating a map of exhaust amount of NO X NOXA.
FIG. 18 is a diagram showing the fuel injection timing.
FIG. 19 is a diagram showing a map of the additional fuel amount WR.
20A and 20B are views showing a hydrocarbon injection period and the like.
21A and 21B are time charts showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
22A and 22B are views showing the structure of the air-fuel ratio sensor shown schematically.
23A and 23B are diagrams showing changes in the air-fuel ratio detected by the downstream air-fuel ratio sensor.
FIG. 24 is a diagram showing a map of peak air-fuel ratio.
FIG. 25 is a time chart showing changes in the peak air-fuel ratio reduction rate.
26A and 26B are diagrams showing changes in the air-fuel ratio detected by the downstream air-fuel ratio sensor and the like.
FIG. 27 is a time chart showing changes in the peak air-fuel ratio reduction rate and the like.
FIG. 28 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
FIG. 29 is a diagram showing a change in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
30 and 31 are flowcharts for performing operation control.
FIG. 32 is a flowchart showing an embodiment of a peak air-fuel ratio detection routine.
FIG. 33 is a flowchart showing another embodiment of the peak air-fuel ratio detection routine.
FIG. 34 is a flowchart showing still another embodiment of the peak air-fuel ratio detection routine.
図1を参照すると、1は機関本体、2は各気筒の燃焼室、3は各燃焼室2内に夫々燃料を噴射するための電子制御式燃料噴射弁、4は吸気マニホルド、5は排気マニホルドを夫々示す。吸気マニホルド4は吸気ダクト6を介して排気ターボチャージャ7のコンプレッサ7aの出口に連結され、コンプレッサ7aの入口は吸入空気量検出器8を介してエアクリーナ9に連結される。吸気ダクト6内にはステップモータにより駆動されるスロットル弁10が配置され、更に吸気ダクト6周りには吸気ダクト6内を流れる吸入空気を冷却するための冷却装置11が配置される。図1に示される実施例では機関冷却水が冷却装置11内に導かれ、機関冷却水によって吸入空気が冷却される。
一方、排気マニホルド5は排気ターボチャージャ7の排気タービン7bの入口に連結される。排気タービン7bの出口は排気管12aを介して排気浄化触媒13の入口に連結され、排気浄化触媒13の出口は排気管12bを介して、排気ガス中に含まれるパティキュレートを捕集するためのパティキュレートフィルタ14に連結される。
排気浄化触媒13上流の排気管12a内には圧縮着火式内燃機関の燃料として用いられる軽油その他の燃料からなる炭化水素を供給するための炭化水素供給弁15が配置される。図1に示される実施例では炭化水素供給弁15から供給される炭化水素として軽油が用いられている。なお、本発明はリーン空燃比のもとで燃焼の行われる火花点火式内燃機関にも適用することができる。この場合、炭化水素供給弁15からは火花点火式内燃機関の燃料として用いられるガソリンその他の燃料からなる炭化水素が供給される。
一方、排気マニホルド5と吸気マニホルド4とは排気ガス再循環(以下、EGRと称す)通路16を介して互いに連結され、EGR通路16内には電子制御式EGR制御弁17が配置される。また、EGR通路16周りにはEGR通路16内を流れるEGRガスを冷却するための冷却装置18が配置される。図1に示される実施例では機関冷却水が冷却装置18内に導かれ、機関冷却水によってEGRガスが冷却される。一方、各燃料噴射弁3は燃料供給管19を介してコモンレール20に連結され、このコモンレール20は電子制御式の吐出量可変な燃料ポンプ21を介して燃料タンク22に連結される。燃料タンク22内に貯蔵されている燃料は燃料ポンプ21によってコモンレール20内に供給され、コモンレール20内に供給された燃料は各燃料供給管19を介して燃料噴射弁3に供給される。
電子制御ユニット30はデジタルコンピュータからなり、双方向性バス31によって互いに接続されたROM(リードオンリメモリ)32、RAM(ランダムアクセスメモリ)33、CPU(マイクロプロセッサ)34、入力ポート35および出力ポート36を具備する。炭化水素供給弁15上流の排気管12a内には、機関から排出された排気ガスの空燃比を検出するための上流側空燃比センサ23が配置されており、排気浄化触媒13下流の排気管12b内には、排気浄化触媒13から流出した排気ガスの空燃比を検出するための下流側空燃比センサ24が配置されている。また、排気浄化触媒13の下流には排気浄化触媒13の温度を検出するための温度センサ24が配置されており、パティキュレートフィルタ14にはパティキュレートフィルタ14の前後の差圧を検出するための差圧センサ26が取付けられている。これら上流側空燃比センサ23、下流側空燃比センサ24、温度センサ25、差圧センサ26および吸入空気量検出器8の出力信号は夫々対応するAD変換器37を介して入力ポート35に入力される。
また、アクセルペダル40にはアクセルペダル40の踏込み量Lに比例した出力電圧を発生する負荷センサ41が接続され、負荷センサ41の出力電圧は対応するAD変換器37を介して入力ポート35に入力される。更に入力ポート35にはクランクシャフトが例えば15°回転する毎に出力パルスを発生するクランク角センサ42が接続される。一方、出力ポート36は対応する駆動回路38を介して燃料噴射弁3、スロットル弁10の駆動用ステップモータ、炭化水素供給弁15、EGR制御弁17および燃料ポンプ21に接続される。
図2は排気浄化触媒13の基体上に担持された触媒担体の表面部分を図解的に示している。この排気浄化触媒13では図2に示されるように例えばアルミナからなる触媒担体50上には貴金属触媒51,52が担持されており、更にこの触媒担体50上にはカリウムK、ナトリウムNa、セシウムCsのようなアルカリ金属、バリウムBa、カルシウムCaのようなアルカリ土類金属、ランタノイドのような希土類および銀Ag、銅Cu、鉄Fe、イリジウムIrのようなNOXに電子を供与しうる金属から選ばれた少なくとも一つを含む塩基性層53が形成されている。排気ガスは触媒担体50上に沿って流れるので貴金属触媒51,52は排気浄化触媒13の排気ガス流通表面上に担持されていると言える。また、塩基性層53の表面は塩基性を呈するので塩基性層53の表面は塩基性の排気ガス流通表面部分54と称される。
一方、図2において貴金属触媒51は白金Ptからなり、貴金属触媒52はロジウムRhからなる。即ち、触媒担体50に担持されている貴金属触媒51,52は白金PtおよびロジウムRhから構成されている。なお、排気浄化触媒13の触媒担体50上には白金PtおよびロジウムRhに加えて更にパラジウムPdを担持させることができるし、或いはロジウムRhに代えてパラジウムPdを担持させることができる。即ち、触媒担体50に担持されている貴金属触媒51,52は白金Ptと、ロジウムRhおよびパラジウムPdの少なくとも一方とにより構成される。
炭化水素供給弁15から排気ガス中に炭化水素が噴射されるとこの炭化水素は排気浄化触媒13において改質される。本発明ではこのとき改質された炭化水素を用いて排気浄化触媒13においてNOXを浄化するようにしている。図3はこのとき排気浄化触媒13において行われる改質作用を図解的に示している。図3に示されるように炭化水素供給弁15から噴射された炭化水素HCは触媒51によって炭素数の少ないラジカル状の炭化水素HCとなる。
図4は炭化水素供給弁15からの炭化水素の供給タイミングと排気浄化触媒13への流入排気ガスの空燃比(A/F)inの変化とを示している。なお、この空燃比(A/F)inの変化は排気浄化触媒13に流入する排気ガス中の炭化水素の濃度変化に依存しているので図4に示される空燃比(A/F)inの変化は炭化水素の濃度変化を表しているとも言える。ただし、炭化水素濃度が高くなると空燃比(A/F)inは小さくなるので図4においては空燃比(A/F)inがリッチ側となるほど炭化水素濃度が高くなっている。
図5は、排気浄化触媒13に流入する炭化水素の濃度を周期的に変化させることによって図4に示されるように排気浄化触媒13への流入排気ガスの空燃比(A/F)inを変化させたときの排気浄化触媒13によるNOX浄化率を排気浄化触媒13の各触媒温度TCに対して示している。本発明者は長い期間に亘ってNOX浄化に関する研究を重ねており、その研究課程において、排気浄化触媒13に流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させると、図5に示されるように400℃以上の高温領域においても極めて高いNOX浄化率が得られることが判明したのである。
更にこのときには窒素および炭化水素を含む多量の還元性中間体が塩基性層53の表面上に、即ち排気浄化触媒13の塩基性排気ガス流通表面部分54上に保持又は吸着され続けており、この還元性中間体が高NOX浄化率を得る上で中心的役割を果していることが判明したのである。次にこのことについて図6Aおよび6Bを参照しつつ説明する。なお、これら図6Aおよび6Bは排気浄化触媒13の触媒担体50の表面部分を図解的に示しており、これら図6Aおよび6Bには排気浄化触媒13に流入する炭化水素の濃度が予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動せしめたときに生ずると推測される反応が示されている。
図6Aは排気浄化触媒13に流入する炭化水素の濃度が低いときを示しており、図6Bは炭化水素供給弁15から炭化水素が供給されて排気浄化触媒13に流入する炭化水素の濃度が高くなっているときを示している。
さて、図4からわかるように排気浄化触媒13に流入する排気ガスの空燃比は一瞬を除いてリーンに維持されているので排気浄化触媒13に流入する排気ガスは通常酸素過剰の状態にある。従って排気ガス中に含まれるNOは図6Aに示されるように白金51上において酸化されてNO2となり、次いでこのNO2は更に酸化されてNO3となる。また、NO2の一部はNO2 −となる。この場合、NO3の生成量の方がNO2 −の生成量よりもはるかに多い。従って白金Pt51上には多量のNO3と少量のNO2 −が生成されることになる。これらNO3およびNO2 −は活性が強く、以下これらNO3およびNO2 −を活性NOX *と称する。
一方、炭化水素供給弁15から炭化水素が供給されると図3に示されるようにこの炭化水素は排気浄化触媒13内において改質され、ラジカルとなる。その結果、図6Bに示されるように活性NOX *周りの炭化水素濃度が高くなる。ところで活性NOX *が生成された後、活性NOX *周りの酸素濃度が高い状態が一定時間以上継続すると活性NOX *は酸化され、硝酸イオンNO3 −の形で塩基性層53内に吸収される。しかしながらこの一定時間が経過する前に活性NOX *周りの炭化水素濃度が高くされると図6Bに示されるように活性NOX *は白金51上においてラジカル状の炭化水素HCと反応し、それにより還元性中間体が生成される。この還元性中間体は塩基性層53の表面上に付着又は吸着される。
なお、このとき最初に生成される還元性中間体はニトロ化合物R−NO2であると考えられる。このニトロ化合物R−NO2は生成されるとニトリル化合物R−CNとなるがこのニトリル化合物R−CNはその状態では瞬時しか存続し得ないのでただちにイソシアネート化合物R−NCOとなる。このイソシアネート化合物R−NCOは加水分解するとアミン化合物R−NH2となる。ただしこの場合、加水分解されるのはイソシアネート化合物R−NCOの一部であると考えられる。従って図6Bに示されるように塩基性層53の表面上に保持又は吸着されている還元性中間体の大部分はイソシアネート化合物R−NCOおよびアミン化合物R−NH2であると考えられる。
一方、図6Bに示されるように生成された還元性中間体の周りを炭化水素HCが取り囲んでいると還元性中間体は炭化水素HCに阻まれてそれ以上反応が進まない。この場合、排気浄化触媒13に流入する炭化水素の濃度が低下せしめられ、それによって酸素濃度が高くなると還元性中間体周りの炭化水素は酸化せしめられる。その結果、図6Aに示されるように還元性中間体と活性NOX *とが反応するようになる。このとき活性NOX *は還元性中間体R−NCOやR−NH2と反応してN2,CO2,H2Oとなり、斯くしてNOXが浄化されることになる。
このように排気浄化触媒13では、排気浄化触媒13に流入する炭化水素の濃度を高くすることにより還元性中間体が生成され、排気浄化触媒13に流入する炭化水素の濃度を低くして酸素濃度を高くすることにより活性NOX *が還元性中間体と反応し、NOXが浄化される。即ち、排気浄化触媒13によりNOXを浄化するには排気浄化触媒13に流入する炭化水素の濃度を周期的に変化させる必要がある。
無論、この場合、還元性中間体を生成するのに十分高い濃度まで炭化水素の濃度を高める必要があり、生成された還元性中間体を活性NOX *と反応させるのに十分低い濃度まで炭化水素の濃度を低下させる必要がある。即ち、排気浄化触媒13に流入する炭化水素の濃度を予め定められた範囲内の振幅で振動させる必要がある。なお、この場合、生成された還元性中間体が活性NOX *と反応するまで、十分な量の還元性中間体R−NCOやR−NH2を塩基性層53上に、即ち塩基性排気ガス流通表面部分54上保持しておかなければならず、そのために塩基性の排気ガス流通表面部分54が設けられている。
一方、炭化水素の供給周期を長くすると炭化水素が供給された後、次に炭化水素が供給されるまでの間において酸素濃度が高くなる期間が長くなり、従って活性NOX *は還元性中間体を生成することなく硝酸塩の形で塩基性層53内に吸収されることになる。これを回避するためには排気浄化触媒13に流入する炭化水素の濃度を予め定められた範囲内の周期でもって振動させることが必要となる。
そこで本発明による実施例では、排気ガス中に含まれるNOXと改質された炭化水素とを反応させて窒素および炭化水素を含む還元性中間体R−NCOやR−NH2を生成するために排気浄化触媒13の排気ガス流通表面上には貴金属触媒51,52が担持されており、生成された還元性中間体R−NCOやR−NH2を排気浄化触媒13内に保持しておくために貴金属触媒51,52周りには塩基性の排気ガス流通表面部分54が形成されており、塩基性の排気ガス流通表面部分54上に保持された還元性中間体R−NCOやR−NH2の還元作用によりNOXが還元され、炭化水素濃度の振動周期は還元性中間体R−NCOやR−NH2を生成し続けるのに必要な振動周期とされる。因みに図4に示される例では噴射間隔が3秒とされている。
炭化水素濃度の振動周期、即ち炭化水素HCの供給周期を上述の予め定められた範囲内の周期よりも長くすると塩基性層53の表面上から還元性中間体R−NCOやR−NH2が消滅し、このとき白金Pt53上において生成された活性NOX *は図7Aに示されるように硝酸イオンNO3 −の形で塩基性層53内に拡散し、硝酸塩となる。即ち、このときには排気ガス中のNOXは硝酸塩の形で塩基性層53内に吸収されることになる。
一方、図7BはこのようにNOXが硝酸塩の形で塩基性層53内に吸収されているときに排気浄化触媒13内に流入する排気ガスの空燃比が理論空燃比又はリッチにされた場合を示している。この場合には排気ガス中の酸素濃度が低下するために反応が逆方向(NO3 −→NO2)に進み、斯くして塩基性層53内に吸収されている硝酸塩は順次硝酸イオンNO3 −となって図7Bに示されるようにNO2の形で塩基性層53から放出される。次いで放出されたNO2は排気ガス中に含まれる炭化水素HCおよびCOによって還元される。
図8は塩基性層53のNOX吸収能力が飽和する少し前に排気浄化触媒13に流入する排気ガスの空燃比(A/F)inを一時的にリッチにするようにした場合を示している。なお、図8に示す例ではこのリッチ制御の時間間隔は1分以上である。この場合には排気ガスの空燃比(A/F)inがリーンのときに塩基性層53内に吸収されたNOXは、排気ガスの空燃比(A/F)inが一時的にリッチにされたときに塩基性層53から一気に放出されて還元される。従ってこの場合には塩基性層53はNOXを一時的に吸収するための吸収剤の役目を果している。
なお、このとき塩基性層53がNOXを一時的に吸着する場合もあり、従って吸収および吸着の双方を含む用語として吸蔵という用語を用いるとこのとき塩基性層53はNOXを一時的に吸蔵するためのNOX吸蔵剤の役目を果していることになる。即ち、この場合には、機関吸気通路、燃焼室2および排気浄化触媒13上流の排気通路内に供給された空気および燃料(炭化水素)の比を排気ガスの空燃比と称すると、排気浄化触媒13は、排気ガスの空燃比がリーンのときにはNOXを吸蔵し、排気ガス中の酸素濃度が低下すると吸蔵したNOXを放出するNOX吸蔵触媒として機能している。
図9は、排気浄化触媒13をこのようにNOX吸蔵触媒として機能させたときのNOX浄化率を示している。なお、図9の横軸は排気浄化触媒13の触媒温度TCを示している。排気浄化触媒13をNOX吸蔵触媒として機能させた場合には図9に示されるように触媒温度TCが300℃から400℃のときには極めて高いNOX浄化率が得られるが触媒温度TCが400℃以上の高温になるとNOX浄化率が低下する。
このように触媒温度TCが400℃以上になるとNOX浄化率が低下するのは、触媒温度TCが400℃以上になると硝酸塩が熱分解してNO2の形で排気浄化触媒13から放出されるからである。即ち、NOXを硝酸塩の形で吸蔵している限り、触媒温度TCが高いときに高いNOX浄化率を得るのは困難である。しかしながら図4から図6A,6Bに示される新たなNOX浄化方法では図6A,6Bからわかるように硝酸塩は生成されず或いは生成されても極く微量であり、斯くして図5に示されるように触媒温度TCが高いときでも高いNOX浄化率が得られることになる。
そこで本発明による実施例では、炭化水素を供給するための炭化水素供給弁15を機関排気通路内に配置し、炭化水素供給弁15下流の機関排気通路内に排気ガス中に含まれるNOXと改質された炭化水素とを反応させるための排気浄化触媒13を配置し、排気浄化触媒13の排気ガス流通表面上には貴金属触媒51,52が担持されていると共に貴金属触媒51,52周りには塩基性の排気ガス流通表面部分54が形成されており、排気浄化触媒13は、排気浄化触媒13に流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させると排気ガス中に含まれるNOXを還元する性質を有すると共に、炭化水素濃度の振動周期をこの予め定められた範囲よりも長くすると排気ガス中に含まれるNOXの吸蔵量が増大する性質を有しており、機関運転時に排気浄化触媒13に流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させ、それにより排気ガス中に含まれるNOXを排気浄化触媒13において還元するようにしている。
即ち、図4から図6A,6Bに示されるNOX浄化方法は、貴金属触媒を担持しかつNOXを吸収しうる塩基性層を形成した排気浄化触媒を用いた場合において、ほとんど硝酸塩を形成することなくNOXを浄化するようにした新たなNOX浄化方法であると言うことができる。実際、この新たなNOX浄化方法を用いた場合には排気浄化触媒13をNOX吸蔵触媒として機能させた場合に比べて、塩基性層53から検出される硝酸塩は極く微量である。なお、この新たなNOX浄化方法を以下、第1のNOX浄化方法と称する。
次に図10から図15を参照しつつこの第1のNOX浄化方法についてもう少し詳細に説明する。
図10は図4に示される空燃比(A/F)inの変化を拡大して示している。なお、前述したようにこの排気浄化触媒13への流入排気ガスの空燃比(A/F)inの変化は同時に排気浄化触媒13に流入する炭化水素の濃度変化を示している。なお、図10においてΔHは排気浄化触媒13に流入する炭化水素HCの濃度変化の振幅を示しており、ΔTは排気浄化触媒13に流入する炭化水素濃度の振動周期を示している。
更に図10において(A/F)bは機関出力を発生するための燃焼ガスの空燃比を示すベース空燃比を表している。言い換えるとこのベース空燃比(A/F)bは炭化水素の供給を停止したときに排気浄化触媒13に流入する排気ガスの空燃比を表している。一方、図10においてXは、生成された活性NOX *が硝酸塩の形で塩基性層53内に吸蔵されることなく還元性中間体の生成のために使用される空燃比(A/F)inの上限を表しており、活性NOX *と改質された炭化水素とを反応させて還元性中間体を生成させるには空燃比(A/F)inをこの空燃比の上限Xよりも低くすることが必要となる。
別の言い方をすると図10のXは活性NOX *と改質された炭化水素とを反応させて還元性中間体を生成させるのに必要な炭化水素の濃度の下限を表しており、還元性中間体を生成するためには炭化水素の濃度をこの下限Xよりも高くする必要がある。この場合、還元性中間体が生成されるか否かは活性NOX *周りの酸素濃度と炭化水素濃度との比率、即ち空燃比(A/F)inで決まり、還元性中間体を生成するのに必要な上述の空燃比の上限Xを以下、要求最小空燃比と称する。
図10に示される例では要求最小空燃比Xがリッチとなっており、従ってこの場合には還元性中間体を生成するために空燃比(A/F)inが瞬時的に要求最小空燃比X以下に、即ちリッチにされる。これに対し、図11に示される例では要求最小空燃比Xがリーンとなっている。この場合には空燃比(A/F)inをリーンに維持しつつ空燃比(A/F)inを周期的に低下させることによって還元性中間体が生成される。
この場合、要求最小空燃比Xがリッチになるかリーンになるかは排気浄化触媒13の酸化力による。この場合、排気浄化触媒13は例えば貴金属51の担持量を増大させれば酸化力が強まり、酸性を強めれば酸化力が強まる。従って排気浄化触媒13の酸化力は貴金属51の担持量や酸性の強さによって変化することになる。
さて、酸化力が強い排気浄化触媒13を用いた場合に図11に示されるように空燃比(A/F)inをリーンに維持しつつ空燃比(A/F)inを周期的に低下させると、空燃比(A/F)inが低下せしめられたときに炭化水素が完全に酸化されてしまい、その結果還元性中間体を生成することができなくなる。これに対し、酸化力が強い排気浄化触媒13を用いた場合に図10に示されるように空燃比(A/F)inを周期的にリッチにさせると空燃比(A/F)inがリッチにされたときに一部の炭化水素は完全に酸化されることなく部分酸化され、即ち炭化水素が改質され、斯くして還元性中間体が生成されることになる。従って酸化力が強い排気浄化触媒13を用いた場合には要求最小空燃比Xはリッチにする必要がある。
一方、酸化力が弱い排気浄化触媒13を用いた場合には図11に示されるように空燃比(A/F)inをリーンに維持しつつ空燃比(A/F)inを周期的に低下させると、一部の炭化水素は完全に酸化されずに部分酸化され、即ち炭化水素が改質され、斯くして還元性中間体が生成される。これに対し、酸化力が弱い排気浄化触媒13を用いた場合に図10に示されるように空燃比(A/F)inを周期的にリッチにさせると多量の炭化水素は酸化されることなく単に排気浄化触媒13から排出されることになり、斯くして無駄に消費される炭化水素量が増大することになる。従って酸化力が弱い排気浄化触媒13を用いた場合には要求最小空燃比Xはリーンにする必要がある。
即ち、要求最小空燃比Xは図12に示されるように排気浄化触媒13の酸化力が強くなるほど低下させる必要があることがわかる。このように要求最小空燃比Xは排気浄化触媒13の酸化力によってリーンになったり、或いはリッチになったりするが、以下要求最小空燃比Xがリッチである場合を例にとって、排気浄化触媒13に流入する炭化水素の濃度変化の振幅や排気浄化触媒13に流入する炭化水素濃度の振動周期について説明する。
さて、ベース空燃比(A/F)bが大きくなると、即ち炭化水素が供給される前の排気ガス中の酸素濃度が高くなると空燃比(A/F)inを要求最小空燃比X以下とするのに必要な炭化水素の供給量が増大し、それに伴って還元性中間体の生成に寄与しなかった余剰の炭化水素量も増大する。この場合、NOXを良好に浄化するためには前述したようにこの余剰の炭化水素を酸化させる必要があり、従ってNOXを良好に浄化するためには余剰の炭化水素量が多いほど多量の酸素が必要となる。
この場合、排気ガス中の酸素濃度を高めれば酸素量を増大することができる。従ってNOXを良好に浄化するためには、炭化水素が供給される前の排気ガス中の酸素濃度が高いときには炭化水素供給後の排気ガス中の酸素濃度を高める必要がある。即ち、炭化水素が供給される前の排気ガス中の酸素濃度が高いほど炭化水素濃度の振幅を大きくする必要がある。
図13は同一のNOX浄化率が得られるときの、炭化水素が供給される前の排気ガス中の酸素濃度と炭化水素濃度の振幅ΔHとの関係を示している。図13から同一のNOX浄化率を得るためには炭化水素が供給される前の排気ガス中の酸素濃度が高いほど炭化水素濃度の振幅ΔHを増大させる必要があることがわかる。即ち、同一のNOX浄化率を得るにはベース空燃比(A/F)bが高くなるほど炭化水素濃度の振幅ΔTを増大させることが必要となる。別の言い方をすると、NOXを良好に浄化するためにはベース空燃比(A/F)bが低くなるほど炭化水素濃度の振幅ΔTを減少させることができる。
ところでベース空燃比(A/F)bが最も低くなるのは加速運転時であり、このとき炭化水素濃度の振幅ΔHが200ppm程度あればNOXを良好に浄化することができる。ベース空燃比(A/F)bは通常、加速運転時よりも大きく、従って図14に示されるように炭化水素濃度の振幅ΔHが200ppm以上であれば良好なNOX浄化率を得ることができることになる。
一方、ベース空燃比(A/F)bが最も高いときには炭化水素濃度の振幅ΔHを10000ppm程度にすれば良好なNOX浄化率が得られることがわかっている。従って本発明では炭化水素濃度の振幅の予め定められた範囲が200ppmから10000ppmとされている。
また、炭化水素濃度の振動周期ΔTが長くなると炭化水素が供給された後、次に炭化水素が供給される間、活性NOX *周りの酸素濃度が高くなる。この場合、炭化水素濃度の振動周期ΔTが5秒程度よりも長くなると活性NOX *が硝酸塩の形で塩基性層53内に吸収され始め、従って図15に示されるように炭化水素濃度の振動周期ΔTが5秒程度よりも長くなるとNOX浄化率が低下することになる。従って炭化水素濃度の振動周期ΔTは5秒以下とする必要がある。
一方、炭化水素濃度の振動周期ΔTがほぼ0.3秒以下になると供給された炭化水素が排気浄化触媒13の排気ガス流通表面上に堆積し始め、従って図15に示されるように炭化水素濃度の振動周期ΔTがほぼ0.3秒以下になるとNOX浄化率が低下する。そこで本発明では炭化水素濃度の振動周期が0.3秒から5秒の間とされている。
次に図16から図19を参照しつつ排気浄化触媒13をNOX吸蔵触媒として機能させた場合のNOX浄化方法について具体的に説明する。このように排気浄化触媒13をNOX吸蔵触媒として機能させた場合のNOX浄化方法を以下、第2のNOX浄化方法と称する。
この第2のNOX浄化方法では図16に示されるように塩基性層53に吸蔵された吸蔵NOX量ΣNOXが予め定められた許容量MAXを越えたときに排気浄化触媒13に流入する排気ガスの空燃比(A/F)inが一時的にリッチにされる。排気ガスの空燃比(A/F)inがリッチにされると排気ガスの空燃比(A/F)inがリーンのときに塩基性層53内に吸蔵されたNOXが塩基性層53から一気に放出されて還元される。それによってNOXが浄化される。
吸蔵NOX量ΣNOXは例えば機関から排出されるNOX量から算出される。本発明による実施例では機関から単位時間当り排出される排出NOX量NOXAが機関出力トルクTeおよび機関回転数Nの関数として図17に示すようなマップの形で予めROM32内に記憶されており、この排出NOX量NOXAから吸蔵NOX量ΣNOXが算出される。この場合、前述したように排気ガスの空燃比(A/F)inがリッチにされる周期は通常1分以上である。
この第2のNOX浄化方法では図18に示されるように燃焼室2内に燃料噴射弁3から出力発生用燃料Qに加え、追加の燃料WRを噴射することによって排気浄化触媒13に流入する排気ガスの空燃比(A/F)inがリッチにされる。なお、図18の横軸はクランク角を示している。この追加の燃料WRは燃焼はするが機関出力となって現われない時期に、即ち圧縮上死点後ATDC90°の少し手前で噴射される。この燃料量WRは機関出力トルクTeおよび機関回転数Nの関数として図19に示すようなマップの形で予めROM32内に記憶されている。無論、この場合炭化水素供給弁15からの炭化水素の供給量を増大させることによって排気ガスの空燃比(A/F)inをリッチにすることもできる。
さて、再び第1のNOX浄化方法についての説明に戻ると、第1のNOX浄化方法を用いてNOXを良好に浄化するためには前述したように炭化水素濃度の振幅ΔHおよび振動周期ΔTを適切に制御する必要がある。即ち、第1のNOX浄化方法を用いてNOXを良好に浄化するためには、排気浄化触媒13への流入排気ガスの空燃比(A/F)inが要求最小空燃比X以下となるように炭化水素濃度の振幅ΔHを制御し、炭化水素濃度の振動周期ΔTを0.3秒から5秒の間に制御する必要がある。
この場合、本発明では炭化水素濃度の振幅ΔHは炭化水素供給弁15からの炭化水素の噴射量を制御することに制御され、炭化水素濃度の振動周期ΔTは炭化水素供給弁15からの炭化水素の噴射周期を制御することによって制御される。この場合、炭化水素供給弁15からの炭化水素の噴射量は、炭化水素供給弁15からの炭化水素の噴射時間又は噴射圧の少なくとも一方を制御することによって制御可能である。しかしながら以下、噴射圧を一定に保持しつつ噴射時間を制御することにより噴射量を制御するようにした場合を例にとって本発明による実施例についての説明を行うこととする。
さて、本発明による実施例では、機関の運転状態に応じた最適なスロットル弁10の開度および最適なEGR制御弁17の開度が予め実験により求められており、更にスロットル弁10およびEGR制御弁17が夫々最適な開度とされているときに得られる最適なベース空燃比(A/F)bも予め実験により求められている。機関運転時には、機関から排出される排気ガスの空燃比がこの最適なベース空燃比(A/F)bとなるように、燃料噴射弁3からの燃料噴射量が制御される。
また、第1のNOX浄化方法によるNOX浄化作用が行われているときに最も高いNOX浄化率の得られる最適な炭化水素噴射周期ΔTと最適な炭化水素噴射時間WTとが実験により予め求められている。この最適な炭化水素噴射周期ΔTは、機関回転数Nおよび機関出力トルクTeの関数として図20Aに示されるようなマップの形で予めROM32内に記憶されており、またこの最適な炭化水素噴射時間WTも、機関回転数Nおよび機関出力トルクTeの関数として図20Bに示されるようなマップの形で予めROM32内に記憶されている。
図21Aは、炭化水素噴射周期を図20Aに示される最適な炭化水素噴射周期ΔTとし、炭化水素噴射時間を図20Bに示される最適な炭化水素噴射時間WTとしたときの排気浄化触媒13への流入排気ガスの空燃比(A/F)inの変化を示しており、図21Bはこのとき下流側空燃比センサ24により検出される空燃比の変化を示している。図21Aおよび図21Bからわかるように、排気浄化触媒13への流入排気ガスの空燃比(A/F)inのリッチ側ピーク空燃比(A/F)rはリッチになっているのに対し、下流側空燃比センサ24により検出された空燃比のリッチ側ピーク空燃比(A/F)pはリーンとなっている。これは、供給された炭化水素の一部が排気浄化触媒13に一旦付着した後に時間差をもって蒸発し、それにより排気浄化触媒13から流出する排気ガスの空燃比の変化が平滑化されるので空燃比のピーク値が小さくなるからであると考えられる。
次に、本発明において用いられている上流側空燃比センサ23および下流側空燃比センサ24の構造について簡単に説明する。なお、これらの上流側空燃比センサ23および下流側空燃比センサ24は同じ構造を有しており、図22Aはこれら空燃比センサ23、24の構造を概略的に示している。
図22Aを参照すると、空燃比センサ23、24のセンサ部60は、ジルコニアZrからなる薄肉カップ状の固体電解質61と、固体電解質61の内周面を覆う白金薄膜電極62と、固体電解質61の外周面を覆う白金薄膜電極63と、電極63の周りを覆うアルミナからなる拡散抵抗層64とに構成されており、このセンサ部60は多数の孔65を有する保護カバー66により覆われている。このセンサ部60は排気ガス中に配置されており、排気ガスは孔65を通って拡散抵抗層64上に導かれる。図22Aに示されるように、電極62と63間には一定電圧Eが印加されており、このとき電極62と63間には排気ガスの空燃比に応じて図22Bに示されるような電流Iが流れる。本発明ではこの電流値Iから図22Bに示される関係に基づいて空燃比が求められる。即ち、空燃比センサ23、24の出力から空燃比が検出される。
ところで排気ガス中にはSOXが含まれており、この場合空燃比センサ23,24はこのSOXの影響を受けるものと考えられる。しかしながら、空燃比センサ23,24により検出された空燃比がこの排気ガス中に含まれるSOXによってどのような影響を受けるかについてはこれまで全く知られていない。そこで本発明者は、空燃比センサ23,24により検出された空燃比が排気ガス中に含まれるSOXによってどのような影響を受けるかについて検討し、その結果空燃比センサ23,24により検出された空燃比と空燃比センサ23,24の硫黄被毒との関係を見つけ出したのである。
次にこのことについて、下流側空燃比センサ24を例にとって説明する。図23Aの実線は、図21Aに示される下流側空燃比センサ24による検出空燃比の変化をそのまま示している。即ち、図23Aの実線は、下流側空燃比センサ24が硫黄被毒を生じていないときに下流側空燃比センサ24によって検出される空燃比の変化を示している。ところが、下流側空燃比センサ24に硫黄成分が付着すると、下流側空燃比センサ24への硫黄成分の付着量が多くなるほど図23Aにおいて破線で示されるように、下流側空燃比センサ24により検出される空燃比の変化量が小さくなると共に空燃比の変化期間が長くなることが判明したのである。
その理由は次のように考えられる。即ち、図22Aに示される空燃比センサでは、排気ガス中に含まれる酸素および炭化水素が拡散抵抗層64内を拡散して電極63に達し、電極63上において炭化水素の酸化作用が行われ、このとき酸素が過剰であれば酸素イオンが固体電解質61内を電極63から62に向けて移動し、このとき酸素が不足していれば酸素イオンが固体電解質61内を電極62から63に向けて移動し、それにより発生する電流Iによって空燃比が検出される。
ところが排気ガス中にSOXが含まれているとこのSOXも拡散抵抗層64内に侵入し、一方では電極63上において白金と反応してPtSを形成し、他方では拡散抵抗層64内においてSO2の形で或いは硫酸イオンの形でアルミナに吸着する。電極63上にPtSが形成されると電極63上における炭化水素の酸化速度が低下せしめられるために電流値Iは長い時間に亘ってゆっくりと変化することになる。また、SOXがアルミナに吸着すると拡散抵抗層64内の細孔が閉塞されるので、分子量の大きな炭化水素は電極63まで拡散するのに時間を有するようになり、従ってこのことによっても電流値Iは長い時間に亘ってゆっくりと変化することになる。従って、下流側空燃比センサ24が硫黄被毒を生ずると、下流側空燃比センサ24により検出される空燃比の変化量が小さくなると共に空燃比の変化期間が長くなることになる。
この場合、下流側空燃比センサ24への硫黄成分の付着量が増大するほどそれに伴って下流側空燃比センサ24により検出される空燃比の変化量が小さくなると共に空燃比の変化期間が長くなり、従って下流側空燃比センサ24により検出される空燃比の変化から下流側空燃比センサ24の硫黄被毒量を検出できることになる。このことは上流側空燃比センサ23についても同様である。
そこで本発明では、空燃比センサ23,24が固体電解質61と、固体電解質61の両側面を夫々覆う電極62,63と、一方の電極63を覆う拡散抵抗層64とを有すると共に排気ガスがこの拡散抵抗層64上に導かれる型式のセンサからなり、排気ガスの空燃比が変化して空燃比センサ23,24により検出される空燃比が変化したとき、空燃比センサ23,24により検出される空燃比の変化が空燃比センサ23,24への硫黄成分の付着量により左右され、このとき空燃比センサ23,24への硫黄成分の付着量が多いほど空燃比センサ23,24により検出される空燃比の変化量が小さくなると共に空燃比の変化期間が長くなり、このときの空燃比センサ23,24により検出される空燃比の変化から空燃比センサ23,24の硫黄被毒量を検出するようにしている。
次に空燃比センサ23、24の硫黄被毒量を検出するための具体的な方法について、再び下流側空燃比センサ24を例にとって説明する。図23Aにおいて破線で示されるように、下流側空燃比センサ24が硫黄被毒を生じると下流側空燃比センサ24により検出された空燃比のリッチ側ピーク空燃比が(A/F)pから(A/F)zに変化する。即ち、下流側空燃比センサ24が硫黄被毒を生じると、ベース空燃比(A/F)bに対する空燃比の変化量がΔAFpからΔAFzに減少する。従って、本発明による一実施例では、下流側空燃比センサ24により検出された空燃比のリッチ側ピーク空燃比から、或いはベース空燃比(A/F)bに対する空燃比の変化量から、下流側空燃比センサ24の硫黄被毒量が検出される。
図23Bは、下流側空燃比センサ24により検出された空燃比のリッチ側ピーク空燃比の低下率ΔAFRと硫黄被毒量との関係を示している。なお、このピーク空燃比低下率ΔAFRは次式でもって表される。
ΔAFR=(ΔAFp−ΔAFz)/ΔAFp
ここで ΔAFp=(A/F)b−(A/F)p
ΔAFz=(A/F)b−(A/F)z
上式において、ベース空燃比(A/F)bは機関の運転状態が定まるとそれに応じて定まる。一方、下流側空燃比センサ24が硫黄被毒を生じていないときに下流側空燃比センサ24により検出されるリッチ側ピーク空燃比(A/F)pは予め実験により求められており、予め実験により求められているこのリッチ側ピーク空燃比(A/F)pは機関回転数Nおよび機関出力トルクTeの関数として図24に示されるようなマップの形で予めROM32内に記憶されている。従って、ΔAFpは機関の運転状態が定まるとそれに応じて定まることになる。
一方、リッチ側ピーク空燃比が(A/F)zは下流側空燃比センサ24により検出された値であり、この検出されたリッチ側ピーク空燃比(A/F)zと機関の運転状態から定まるベース空燃比(A/F)bからΔAFzが算出される。即ち、ピーク空燃比低下率ΔAFRは下流側空燃比センサ24により検出されたリッチ側ピーク空燃比(A/F)zから算出されることになる。図23Bに示されるようにピーク空燃比低下率ΔAFRが増大するほど下流側空燃比センサ24の硫黄被毒量が大きくなる。
さて、排気ガス中に硫黄が含まれていると図25において実線で示されるように、時間の経過に伴い、ピーク空燃比低下率ΔAFRは次第に大きくなっていく。一方、炭化水素供給弁15が目詰まりを生じ、炭化水素の供給量が低下したときにも下流側空燃比センサ24により検出されるリッチ側ピーク空燃比(A/F)zが大きくなり、その結果ピーク空燃比低下率ΔAFRが増大する。しかしながら炭化水素供給弁15の目詰まりは比較的急激に生じ、一旦目詰まりを生ずると図25において破線で示されるようにそれほど変化しなくなるので、ピーク空燃比低下率ΔAFRの時間的な変化を監視し続けると、下流側空燃比センサ24の硫黄被毒によってピーク空燃比低下率ΔAFRが大きくなったのか、炭化水素供給弁15の目詰まりによってピーク空燃比低下率ΔAFRが大きくなったのかを判別できることになる。
そこで本発明による実施例では、ピーク空燃比低下率ΔAFRの時間的な変化から、即ち下流側空燃比センサ24により検出される空燃比の変化から、下流側空燃比センサ24が硫黄被毒をしたのか或いは炭化水素供給弁15が目詰まりをしたのかを判別するようにしている。
次に、図26Aを参照しつつ別の実施例について説明する。この実施例では下流側空燃比センサ24により検出される空燃比とベース空燃比(A/F)bとの差の積分値から下流側空燃比センサ24の硫黄被毒量を求めるようにしている。即ち、炭化水素供給弁15から炭化水素が一回噴射され、排気浄化触媒13に流入する排気ガスの空燃比が瞬時的に変化したときに、下流側空燃比センサ24が硫黄被毒していない場合には、図26Aにおいて実線で示されるように下流側空燃比センサ24により検出される空燃比は図26AのAで示される予め定められた期間内で瞬時的に変化を完了する。
これに対し、下流側空燃比センサ24が硫黄被毒をしている場合には、図26Aにおいて破線で示されるように下流側空燃比センサ24により検出される空燃比は予め定められた期間Aを超えて変化し続ける。なお、この予め定められた期間Aは、下流側空燃比センサ24が硫黄被毒していない場合において、炭化水素供給弁15から炭化水素が一回噴射されたときに、下流側空燃比センサ24により検出される空燃比の瞬時的な変化がほぼ完了する期間である。
この実施例では、図26Aにおいて、予め定められた期間A内における下流側空燃比センサ24により検出される空燃比とベース空燃比(A/F)bとの差の積分値SA、即ち面積SAと、これら期間Aと期間Aとの間の期間B内における下流側空燃比センサ24により検出される空燃比とベース空燃比(A/F)bとの差の積分値SB、即ち面積SBとが算出される。この場合、図26Aから、実線で示されるように下流側空燃比センサ24が硫黄被毒していない場合には、面積SAは大きいが面積SBはほとんど零となり、これに対し破線で示されるように下流側空燃比センサ24が硫黄被毒をしている場合には、面積SAは小さくなり、面積SBは大きくなることがわかる。
即ち、下流側空燃比センサ24の硫黄被毒量は面積SAに対する面積SBの比に顕著に現れることがわかる。図26Bは、面積SAに対する面積SBの比SB/SAと硫黄被毒量との関係を示しており、この比SB/SAが大きくなるほど硫黄被毒量が大きくなることがわかる。
そこで本発明による実施例では、下流側空燃比センサ24により検出される空燃比とベース空燃比(A/F)bとの差の積分値SA,SBが算出されており、排気ガスの空燃比が瞬時的に変化したときに下流側空燃比センサ24により検出される空燃比は、下流側空燃比センサ24が硫黄被毒をしていなければ予め定められた期間A内で瞬時的に変化を完了するが下流側空燃比センサ24の硫黄被毒量が増大すると予め定められた期間Aを超えて変化し続け、予め定められた期間A内における積分値SAと予め定められた期間Aを超えているときの積分値SBとの比SB/SAから下流側空燃比センサ24の硫黄被毒量を検出するようにしている。
この場合、積分値SAの値としては空燃比が複数回変動する間の平均値を用いることができ、積分値SBの値についても空燃比が複数回変動する間の平均値を用いることができる。
このように下流側空燃比センサ24の硫黄被毒量は、下流側空燃比センサ24により検出されたリッチ側ピーク空燃比(A/F)zから求めることもできるし、下流側空燃比センサ24により検出される空燃比とベース空燃比(A/F)bとの差の積分値SA,SBの比SB/SAから求めることもできる。従って、これらを包括的に表現すると、硫黄被毒を生じていないときの下流側空燃比センサ24により検出される空燃比の変化を代表する値が基準値として予め求められており、この基準値に対する、下流側空燃比センサ24により検出された空燃比の変化を代表する値から下流側空燃比センサ24の硫黄被毒量が検出される。
この場合、図23Aに示される実施例では、下流側空燃比センサ24により検出される空燃比の変化を代表する値がリッチ側ピーク空燃比が(A/F)zであり、基準値が図24に示される予め記憶されているリッチ側ピーク空燃比(A/F)pである。一方、図26Aに示される実施例では、下流側空燃比センサ24により検出される空燃比の変化を代表する値が予め定められた期間A内における積分値SAと予め定められた期間Aを超えているときの積分値SBとの比SB/SAであり、この場合の基準値はほぼ零(SB/SA≒0)である。
ところでこれら基準値は予め求めておくこともできるし、また実測することもできる。ただし後者の場合には、即ち基準値を実測するようにした場合には、下流側空燃比センサ24が硫黄被毒していたときには、基準値を実測する前に硫黄被毒の回復処理をしておくことが必要となる。次にこのことについて、下流側空燃比センサ24の硫黄被毒量をリッチ側ピーク空燃比(A/F)zから求めるようにした場合を例にとって図27を参照しつつ説明する。
図27を参照すると、ピーク空燃比低下率ΔAFRが予め定められた許容値RXに達すると下流側空燃比センサ24の硫黄被毒の回復処理が行われる。この場合、下流側空燃比センサ24に付着したSOXは下流側空燃比センサ24の温度が650℃程度のSOX分解温度を超えると下流側空燃比センサ24から放出され、また下流側空燃比センサ24に付着したSOXは下流側空燃比センサ24に流入する排気ガスの空燃比がリッチとされかつ下流側空燃比センサ24の温度が500℃程度のSOX放出温度を超えると下流側空燃比センサ24から放出される。従って、下流側空燃比センサ24からSOXを放出すべきときには、即ち下流側空燃比センサ24の硫黄被毒を回復すべきときには、下流側空燃比センサ24の温度が650℃程度のSOX分解温度まで上昇せしめられるか、或いは下流側空燃比センサ24の温度が500℃程度のSOX放出温度まで上昇せしめられかつ下流側空燃比センサ24に流入する排気ガスの空燃比がリッチとされる。
図27に示されるように、下流側空燃比センサ24の硫黄被毒の回復処理が完了すると、下流側空燃比センサ24により検出された空燃比に基づき、基準値となるリッチ側ピーク空燃比(A/F)pが検出される。なお、このリッチ側ピーク空燃比(A/F)pは炭化水素の供給量が同一であっても下流側空燃比センサ24の温度、即ち排気ガスの温度が変化し、排気ガスの流量が変化するとそれに伴って変化する。従って、本発明による実施例では、排気ガスの温度が予め定められた温度範囲内でありかつ排気ガスの流量、即ち吸入空気量が予め定められた流量範囲内であるときがリッチ側ピーク空燃比(A/F)pを検出するための検出条件であるとされており、この検出条件が満たされるときに下流側空燃比センサ24により検出された空燃比に基づき、基準値となるリッチ側ピーク空燃比(A/F)pが検出される。
図27に示されるように、この基準値となるリッチ側ピーク空燃比(A/F)pが検出されると、その後この検出条件が満たされる毎に、下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)zが検出され、これらリッチ側ピーク空燃比(A/F)pおよび(A/F)zからピーク空燃比低下率ΔAFRが算出される。なお、本発明による実施例では、例えば、硫黄濃度の高い燃料が用いられたとすると、図27において破線で示されるようにピーク空燃比低下率ΔAFRが急速に変化するようになり、ピーク空燃比低下率ΔAFRが許容値RXに達する間隔が短くなる。従って、このことから硫黄濃度の高い燃料が用いられたことを検知することができることになる。
また、炭化水素供給弁15からの炭化水素の供給量を増大すると下流側空燃比センサ24により検出される空燃比の変化が大きくなり、その結果リッチ側ピーク空燃比(A/F)zの変化を、より正確に検出できるようになる。従って、本発明による実施例では図28に示されるように、基準値となるリッチ側ピーク空燃比(A/F)pおよびリッチ側ピーク空燃比(A/F)zの検出時には、炭化水素供給弁15からの炭化水素の供給量が機関の運転状態から定まる炭化水素供給量に比べて増大される。即ち、排気ガスの空燃比のリッチ側ピーク空燃比が更にリッチ側とされる。
さて、排気ガス中にSO2が含まれているとこのSO2は白金Pt53上において酸化されてSO3となる。次いでこのSO3は塩基性層53内に吸蔵されて硫酸イオンSO4 2−の形で塩基性層53内に拡散し、安定した硫酸塩を生成する。しかしながらこの硫酸塩は安定していて分解しづらく、排気ガスの空燃比を単にリッチにしただけでは硫酸塩は分解されずにそのまま残る。この場合、吸蔵されている硫酸塩の吸蔵量が増大するとNOX浄化率が低下する。従って、硫酸塩の吸蔵量が増大したときには排気浄化触媒13から吸蔵されているSOXを放出させる必要がある。
ところでこの場合、排気浄化触媒13の温度を650℃程度のSOX分解温度まで上昇させるか、或いは排気浄化触媒13の温度を500℃程度のSOX放出温度まで上昇させかつ排気浄化触媒13に流入する排気ガスの空燃比をリッチにすると、排気浄化触媒13から吸蔵されているSOXを放出させることができる。
そこで本発明による実施例では、排気浄化触媒13から吸蔵されているSOXを放出すべきときには、燃焼室2内への追加の燃料量WRを制御することによって排気浄化触媒13への流入排気ガスの空燃比(A/F)inを図29に示されるように交互にリッチとリーンに切り替え、それにより排気浄化触媒13の温度を500℃程度のSOX放出温度まで上昇させかつ排気浄化触媒13に流入する排気ガスの空燃比を間欠的にリッチにさせて排気浄化触媒13から吸蔵されているSOXを放出させるようにしている。
一方、前述したように、本発明では下流側空燃比センサ24により検出された空燃比に基づいて下流側空燃比センサ24の硫黄被毒量が算出される。ところが下流側空燃比センサ24へのSOXの付着量が増大すれば排気浄化触媒13へのSOXの吸蔵量も増大する。即ち、空燃比センサの硫黄被毒量から排気浄化触媒13の硫黄被毒量を推定できることになる。そこで本発明による実施例では、空燃比センサにより検出される空燃比の変化から排気浄化触媒13の硫黄被毒量を推定するようにしている。具体的に言うと、本発明による実施例では、下流側空燃比センサ24の硫黄被毒量から排気浄化触媒13の硫黄被毒量を推定するようにしている。この場合、本発明による実施例では、ピーク空燃比低下率ΔAFRが許容値を超えたときには排気浄化触媒13の硫黄被毒も許容値を超えたと判断され、このとき排気浄化触媒13から吸蔵されているSOXを放出させるために、排気浄化触媒13への流入排気ガスの空燃比(A/F)inが図29に示されるように交互にリッチとリーンに切り替えられる。
次に、図30および31に示される機関の運転制御ルーチンについて説明する。なお、このルーチンは一定時間毎の割込みによって実行される。
図30を参照するとまず初めにステップ70において温度センサ25の出力信号から排気浄化触媒13の温度TCが活性化温度TCoを越えているか否かが判別される。TC<TCoのとき、即ち排気浄化触媒13が活性化していないときには第2のNOX浄化方法を用いるべきであると判断され、ステップ71に進む。ステップ71では図17に示すマップから単位時間当りの排出NOX量NOXAが算出される。次いでステップ72ではΣNOXに排出NOX量NOXAを加算することによって吸蔵NOX量ΣNOXが算出される。次いでステップ73では吸蔵NOX量ΣNOXが許容値MAXを越えたか否かが判別される。
ステップ73においてΣNOX≦MAXであると判断されたときにはステップ74に進んで燃料噴射弁3からの燃料噴射処理が行われる。このときには機関の運転状態から定まる予め定められたリーン空燃比となるように燃料噴射弁3から燃料が噴射される。これに対し、ステップ73においてΣNOX>MAXであると判別されたときにはステップ75に進んでリッチ制御Iが行われる。即ち、図19に示すマップから追加の燃料量WRが算出され、追加の燃料の噴射作用が行われる。このとき排気浄化触媒13から吸蔵されたNOXが放出される。次いでステップ76ではΣNOXがクリアされる。
一方、ステップ70においてTC≧TCoになったと判断されたとき、即ち排気浄化触媒13が活性化したときにはステップ77に進み、前回の割り込み時にはTC<TCoであったか否かが判別される。前回の割り込み時にはTC<TCoであったとき、即ち、今排気浄化触媒13が活性化したときにはステップ78に進んでリッチ制御IIが実行される。このときにも図19に示すマップから追加の燃料量WRが算出され、追加の燃料の噴射作用が行われて排気浄化触媒13から吸蔵されたNOXが放出される。次いでステップ79ではΣNOXがクリアされる。
これに対し、前回の割り込み時にもTC≧TCoであったときには、即ち排気浄化触媒13が既に活性化しているときにはステップ80に進み、本発明による第1のNOX浄化方法によるNOX浄化作用が行われる。即ち、排気浄化触媒13が活性化していないときには第2のNOX浄化方法によるNOX浄化作用が行われており、排気浄化触媒13が活性化すると第2のNOX浄化方法から第1のNOX浄化方法へ切り替えられる。
第2のNOX浄化方法から第1のNOX浄化方法に切り替えられたときに排気浄化触媒13にNOXが吸蔵していると、排気浄化触媒13から吸蔵されているNOXが還元されることなく一気に放出される。従って図30に示される例では、このように排気浄化触媒13から吸蔵されているNOXが還元されることなく一気に放出されるのを阻止するために、第2のNOX浄化方法から第1のNOX浄化方法に切り替えられる直前にステップ78において第2のNOX浄化方法により排気浄化触媒13から吸蔵NOXを放出させるためのリッチ制御IIが行われる。
さて、図31を参照すると、まず初めにステップ80においてパティキュレートフィルタ14の再生中であるか否かが判別される。パティキュレートフィルタ14の再生中でないときにはステップ81に進んで差圧センサ26の出力信号からパティキュレートフィルタ14の前後の差圧ΔPが予め定められた限界値PXを超えたか否かが判別される。ΔP≦PXのときにはステップ83に進んで排気浄化触媒13から吸蔵されているSOXを放出させる処理、即ち排気浄化触媒13の硫黄被毒の回復処理が行われているか否かが判別される。排気浄化触媒13の硫黄被毒回復処理中でないときにはステップ84に進んでピーク空燃比低下率ΔAFRが算出され、算出されたピーク空燃比低下率ΔAFRが許容値RXを超えているか否かが判別される。ΔAFR≦RXのときにはステップ86に進む。
ステップ86および87では、上流側空燃比センサ23の出力信号に基づいて、機関から排出される排気ガスの空燃比が予め定められた空燃比となるように機関燃焼室2に供給される燃料の量が制御され、下流側空燃比センサ24の出力信号に基づいて、排気浄化触媒13に流入する炭化水素の濃度変化の振幅が予め定められた範囲内の振幅となるように炭化水素供給弁15からの炭化水素の噴射量が制御される。
具体的に言うと、ステップ86では、上流側空燃比センサ23の出力信号に基づいて機関から排出される排気ガスの空燃比が機関の運転状態に応じた最適なベース空燃比(A/F)bとなるように、燃料噴射弁3からの燃料噴射量が制御される。次いでステップ87では、下流側空燃比センサ24の出力信号に基づくフィードバック制御により第1のNOX浄化方法によるNOX浄化作用が行われる。即ち、炭化水素噴射周期を図20Aに示される最適な炭化水素噴射周期ΔTとし、炭化水素噴射時間を図20Bに示される最適な炭化水素噴射時間WTとしたときに下流側空燃比センサ24により検出されるリッチ側ピーク空燃比が目標ピーク空燃比として予め記憶されており、ステップ87では下流側空燃比センサ24により検出されるリッチ側ピーク空燃比が目標ピーク空燃比となるように炭化水素供給弁15からの炭化水素の噴射時間がフィードバック制御される。
一方、ステップ81においてΔP>PXであると判別されたときにはステップ83に進んでパティキュレートフィルタ14の再生処理が行われる。次いで処理サイクルを完了する。また、ステップ84においてΔAFR>RXであると判別されたときにはステップ85に進んで排気浄化触媒13から吸蔵されているSOXを放出させる処理、即ち排気浄化触媒13の硫黄被毒を回復する処理が行われる。このとき同時に下流側空燃比センサ24の硫黄被毒も回復される。
さて、前述したようにピーク空燃比低下率ΔAFRは基準値に基づいて算出されており、この基準値は予め求めておくこともできるし、実測することもできる。ただし基準値を実測するようにした場合には、前述したように基準値を実測する前に下流側空燃比センサ24の硫黄被毒の回復処理をしておくことが必要となる。このときには、即ち下流側空燃比センサ24の硫黄被毒を回復すべきときには、前述したように、下流側空燃比センサ24の温度が650℃程度のSOX分解温度まで上昇せしめられるか、或いは下流側空燃比センサ24の温度が500℃程度のSOX放出温度まで上昇せしめられかつ下流側空燃比センサ24に流入する排気ガスの空燃比がリッチとされる。
次に、この基準値を実測するためのいくつかの例について説明する。
前述したように排気浄化触媒13の硫黄被毒回復処理が行われると下流側空燃比センサ24の硫黄被毒も回復される。従って、最初の例では、排気浄化触媒13の硫黄被毒回復処理が完了した後、検出条件が満たされたときに下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)pが検出される。なお、前述したように、排気ガスの温度が予め定められた温度範囲内でありかつ排気ガスの流量、即ち吸入空気量が予め定められた流量範囲内であるときに検出条件が満たされていると判断される。
図32はこの例を実行するためのリッチ側ピーク空燃比(A/F)pおよび(A/F)zの検出ルーチンを示しており、このルーチンは一定時間毎の割り込みによって実行される。
図32を参照すると、まず初めにステップ100において排気浄化触媒13の硫黄被毒回復処理中であるか否かが判別され、排気浄化触媒13の硫黄被毒回復処理中であるときには処理サイクルを完了する。これに対し、排気浄化触媒13の硫黄被毒回復処理中でないときにはステップ101に進んで検出条件を満たしているか否かが判別される。このとき検出条件を満たしていなければ処理サイクルを完了する。これに対し、検出条件を満たしているときにはステップ102に進み、下流側空燃比センサ24によって基準となるリッチ側ピーク空燃比(A/F)pの検出が完了したか否かが判別される。リッチ側ピーク空燃比(A/F)pの検出が完了していないときにはステップ103に進んで、排気浄化触媒13の硫黄被毒回復処理が完了してから一定時間が経過したか否かが判別される。排気浄化触媒13の硫黄被毒回復処理が完了してから一定時間が経過していないときにはステップ104に進んで下流側空燃比センサ24により基準となるリッチ側ピーク空燃比(A/F)pが検出される。
即ち、排気浄化触媒13の硫黄被毒回復処理が完了してから一定時間が経過していないときには下流側空燃比センサ24は硫黄被毒をしていないと考えられる。従って、排気浄化触媒13の硫黄被毒回復処理が完了してから一定時間が経過していないときに検出条件が満たされたときには、基準となるリッチ側ピーク空燃比(A/F)pが検出される。一方、ステップ102において基準となるリッチ側ピーク空燃比(A/F)pの検出が完了したと判別されたとき、或いはステップ103において排気浄化触媒13の硫黄被毒回復処理が完了してから一定時間が経過していると判別されたときにはステップ105に進んで下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)zが検出される。即ち、検出条件が満たされる毎にリッチ側ピーク空燃比(A/F)zが検出される。ピーク空燃比低下率ΔAFRは、最新の基準となるリッチ側ピーク空燃比(A/F)pおよび最新のリッチ側ピーク空燃比(A/F)zから図31のステップ84において算出される。
一方、パティキュレートフィルタ14の再生時には炭化水素の供給量が増大せしめられてパティキュレートフィルタ14の温度が650℃程度まで上昇せしめられる。従って、パティキュレートフィルタ14の再生処理が行われると下流側空燃比センサ24の硫黄被毒も回復されることになる。従って、二つ目の例では、パティキュレートフィルタ14の再生処理が完了した後、検出条件が満たされたときに下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)pが検出される。
図33はこの二つ目の例を実行するためのリッチ側ピーク空燃比(A/F)pおよび(A/F)zの検出ルーチンを示しており、このルーチンも一定時間毎の割り込みによって実行される。
図33を参照すると、まず初めにステップ110においてパティキュレートフィルタ14の再生処理中であるか否かが判別され、パティキュレートフィルタ14の再生処理中であるときには処理サイクルを完了する。これに対し、パティキュレートフィルタ14の再生処理中でないときにはステップ111に進んで検出条件を満たしているか否かが判別される。このとき検出条件を満たしていなければ処理サイクルを完了する。これに対し、検出条件を満たしているときにはステップ112に進み、下流側空燃比センサ24によって基準となるリッチ側ピーク空燃比(A/F)pの検出が完了したか否かが判別される。リッチ側ピーク空燃比(A/F)pの検出が完了していないときにはステップ113に進んで、パティキュレートフィルタ14の再生処理が完了してから一定時間が経過したか否かが判別される。パティキュレートフィルタ14の再生処理が完了してから一定時間が経過していないときにはステップ114に進んで下流側空燃比センサ24により基準となるリッチ側ピーク空燃比(A/F)pが検出される。
即ち、パティキュレートフィルタ14の再生処理が完了してから一定時間が経過していないときには下流側空燃比センサ24は硫黄被毒をしていないと考えられる。従って、パティキュレートフイルタ14の再生処理が完了してから一定時間が経過していないときに検出条件が満たされたときには、基準となるリッチ側ピーク空燃比(A/F)pが検出される。一方、ステップ112において基準となるリッチ側ピーク空燃比(A/F)pの検出が完了したと判別されたとき、或いはステップ113においてパティキュレートフィルタ14の再生処理が完了してから一定時間が経過していると判別されたときにはステップ115に進んで下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)zが検出される。即ち、この場合も、検出条件が満たされる毎にリッチ側ピーク空燃比(A/F)zが検出される。ピーク空燃比低下率ΔAFRはこれら最新の基準となるリッチ側ピーク空燃比(A/F)pおよび最新のリッチ側ピーク空燃比(A/F)zから算出される。
一方、前述したように排気浄化触媒13が活性化する前は第2のNOX浄化方法によるNOX浄化作用が行われ、このとき塩基性層53に吸蔵された吸蔵NOX量ΣNOXが予め定められた許容量MAXを越えると排気浄化触媒13に流入する排気ガスの空燃比(A/F)inを一時的にリッチにするリッチ処理が行われる。この場合、もしこのリッチ処理が機関高負荷に行われたとすると、このとき下流側空燃比センサ24の温度は500℃程度のSOX放出温度まで上昇せしめられかつ下流側空燃比センサ24に流入する排気ガスの空燃比がリッチとなる。従って、このときには下流側空燃比センサ24の硫黄被毒が回復されることになる。
従って、三つ目の例では、機関高負荷運転時にリッチ処理が行われた場合には、リッチ処理が完了した後、検出条件が満たされたときに下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)pが検出される。
図34はこの三つ目の例を実行するためのリッチ側ピーク空燃比(A/F)pおよび(A/F)zの検出ルーチンを示しており、このルーチンも一定時間毎の割り込みによって実行される。
図34を参照すると、まず初めにステップ120において機関高負荷運転時でのリッチ処理中であるか否かが判別され、リッチ処理中であるときには処理サイクルを完了する。これに対し、リッチ処理中でないときにはステップ121に進んで検出条件を満たしているか否かが判別される。このとき検出条件を満たしていなければ処理サイクルを完了する。これに対し、検出条件を満たしているときにはステップ122に進み、下流側空燃比センサ24によって基準となるリッチ側ピーク空燃比(A/F)pの検出が完了したか否かが判別される。リッチ側ピーク空燃比(A/F)pの検出が完了していないときにはステップ123に進んで、リッチ処理が完了してから一定時間が経過したか否かが判別される。リッチ処理が完了してから一定時間が経過していないときにはステップ124に進んで下流側空燃比センサ24により基準となるリッチ側ピーク空燃比(A/F)pが検出される。
即ち、機関高負荷運転時でのリッチ処理が完了してから一定時間が経過していないときには下流側空燃比センサ24は硫黄被毒をしていないと考えられる。従って、リッチ処理が完了してから一定時間が経過していないときに検出条件が満たされたときには、基準となるリッチ側ピーク空燃比(A/F)pが検出される。一方、ステップ122において基準となるリッチ側ピーク空燃比(A/F)pの検出が完了したと判別されたとき、或いはステップ123においてリッチ処理が完了してから一定時間が経過していると判別されたときにはステップ125に進んで下流側空燃比センサ24により検出された空燃比からリッチ側ピーク空燃比(A/F)zが検出される。即ち、この場合も、検出条件が満たされる毎にリッチ側ピーク空燃比(A/F)zが検出される。ピーク空燃比低下率ΔAFRはこれら最新の基準となるリッチ側ピーク空燃比(A/F)pおよび最新のリッチ側ピーク空燃比(A/F)zから算出される。
なお、別の実施例として排気浄化触媒13上流の機関排気通路内に炭化水素を改質させるための酸化触媒を配置することもできる。 Fig. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each
On the other hand, the
In the
On the other hand, the
The
A
FIG. 2 schematically shows the surface portion of the catalyst carrier carried on the substrate of the
On the other hand, in FIG. 2, the
When hydrocarbons are injected into the exhaust gas from the
FIG. 4 shows the supply timing of hydrocarbons from the
FIG. 5 shows a change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the
Further, at this time, a large amount of the reducing intermediate containing nitrogen and hydrocarbon continues to be held or adsorbed on the surface of the
FIG. 6A shows a case where the concentration of hydrocarbons flowing into the
As can be seen from FIG. 4, since the air-fuel ratio of the exhaust gas flowing into the
On the other hand, when hydrocarbons are supplied from the
The first reducing intermediate produced at this time is the nitro compound R-NO.2It is thought that. This nitro compound R-NO2Is produced, it becomes a nitrile compound R-CN, but this nitrile compound R-CN can only survive for a moment in that state, so it immediately becomes an isocyanate compound R-NCO. When this isocyanate compound R-NCO is hydrolyzed, the amine compound R-NH2It becomes. However, in this case, it is considered that a part of the isocyanate compound R-NCO is hydrolyzed. Therefore, as shown in FIG. 6B, most of the reducing intermediates retained or adsorbed on the surface of the
On the other hand, as shown in FIG. 6B, when the hydrocarbon HC surrounds the generated reducing intermediate, the reducing intermediate is blocked by the hydrocarbon HC and the reaction does not proceed further. In this case, the concentration of hydrocarbons flowing into the
In this way, in the
Of course, in this case, it is necessary to increase the concentration of hydrocarbons to a concentration sufficiently high to produce a reducing intermediate, and the produced reducing intermediate is activated NO.X *It is necessary to reduce the hydrocarbon concentration to a concentration low enough to react with. That is, it is necessary to vibrate the concentration of hydrocarbons flowing into the
On the other hand, if the hydrocarbon supply cycle is lengthened, the period during which the oxygen concentration becomes high after the hydrocarbon is supplied and until the next hydrocarbon is supplied becomes longer, so that the active NO.X *Is absorbed in the
Therefore, in the embodiment according to the present invention, NO contained in the exhaust gas.XReductive intermediates R-NCO and R-NH containing nitrogen and hydrocarbons by reacting with modified hydrocarbons2In order to generate NO,
When the oscillation period of hydrocarbon concentration, that is, the supply period of hydrocarbon HC is longer than the period within the above-mentioned predetermined range, the reducing intermediates R-NCO and R-NH are formed on the surface of the basic layer 53.2Disappears, and at this time, the active NO produced on platinum Pt53X *Is nitrate ion NO as shown in FIG. 7A.3 −In the form of nitrate in the form of nitrate. That is, at this time, NO in the exhaust gasXWill be absorbed in the
On the other hand, FIG.XThis shows a case where the air-fuel ratio of the exhaust gas flowing into the
Fig. 8 shows NO in
At this time, the
FIG. 9 shows that the
¡If the catalyst temperature TC reaches 400 ° C or higher, NOXThe purification rate decreases because when the catalyst temperature TC reaches 400 ° C. or higher, the nitrate is thermally decomposed and NO.2This is because it is discharged from the
Therefore, in the embodiment according to the present invention, the
That is, the NO shown in FIGS. 4 to 6A and 6BXThe purification method carries a noble metal catalyst and NO.XIn the case of using an exhaust purification catalyst having a basic layer capable of absorbing NO, NO hardly forms nitrates.XNew NO to purifyXIt can be said that it is a purification method. In fact, this new NOXWhen the purification method is used, the
Next, referring to FIG. 10 to FIG.XThe purification method will be described in a little more detail.
FIG. 10 shows an enlarged view of the change in the air-fuel ratio (A / F) in shown in FIG. As described above, the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the
Further, in FIG. 10, (A / F) b represents the base air-fuel ratio indicating the air-fuel ratio of the combustion gas for generating the engine output. In other words, the base air-fuel ratio (A / F) b represents the air-fuel ratio of the exhaust gas flowing into the
In other words, X in Fig. 10 is active NOX *Represents the lower limit of the hydrocarbon concentration required to produce a reducing intermediate by reacting the modified hydrocarbon with the modified hydrocarbon. It is necessary to make it higher than the lower limit X. In this case, whether or not a reducing intermediate is generated depends on the active NO.X *The ratio between the surrounding oxygen concentration and the hydrocarbon concentration, that is, the air-fuel ratio (A / F) in, is determined by the above-mentioned upper limit X of the air-fuel ratio necessary for generating the reducing intermediate, Called.
In the example shown in FIG. 10, the required minimum air-fuel ratio X is rich. Therefore, in this case, the air-fuel ratio (A / F) in is instantaneously required to generate the reducing intermediate. The following is made rich: On the other hand, in the example shown in FIG. 11, the required minimum air-fuel ratio X is lean. In this case, the reducing intermediate is generated by periodically reducing the air-fuel ratio (A / F) in while maintaining the air-fuel ratio (A / F) in lean.
In this case, whether the required minimum air-fuel ratio X becomes rich or lean depends on the oxidizing power of the
When the
On the other hand, when the
That is, it can be seen that the required minimum air-fuel ratio X needs to be lowered as the oxidizing power of the
When the base air-fuel ratio (A / F) b increases, that is, when the oxygen concentration in the exhaust gas before the hydrocarbons are supplied increases, the air-fuel ratio (A / F) in is made equal to or less than the required minimum air-fuel ratio X. As a result, the amount of hydrocarbons necessary for the increase increases, and the amount of excess hydrocarbons that did not contribute to the production of the reducing intermediate also increases. In this case, NOXAs described above, it is necessary to oxidize the surplus hydrocarbons in order to purify the water well.XIn order to purify the water well, a larger amount of excess hydrocarbon requires more oxygen.
In this case, the amount of oxygen can be increased by increasing the oxygen concentration in the exhaust gas. Therefore NOXIn order to purify the gas well, it is necessary to increase the oxygen concentration in the exhaust gas after the hydrocarbon is supplied when the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is high. That is, it is necessary to increase the amplitude of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher.
Figure 13 shows the same NOXIt shows the relationship between the oxygen concentration in the exhaust gas before the hydrocarbon is supplied and the amplitude ΔH of the hydrocarbon concentration when the purification rate is obtained. The same NO from FIG.XIt can be seen that in order to obtain the purification rate, it is necessary to increase the amplitude ΔH of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher. That is, the same NOXIn order to obtain the purification rate, it is necessary to increase the amplitude ΔT of the hydrocarbon concentration as the base air-fuel ratio (A / F) b increases. In other words, NOXIn order to purify the gas well, the amplitude ΔT of the hydrocarbon concentration can be reduced as the base air-fuel ratio (A / F) b becomes lower.
By the way, the base air-fuel ratio (A / F) b is the lowest during acceleration operation, and if the hydrocarbon concentration amplitude ΔH is about 200 ppm, NOXCan be purified well. The base air-fuel ratio (A / F) b is usually larger than that during acceleration operation. Therefore, as shown in FIG. 14, when the hydrocarbon concentration amplitude ΔH is 200 ppm or more, good NO is obtained.XA purification rate can be obtained.
On the other hand, when the base air-fuel ratio (A / F) b is the highest, if the amplitude ΔH of the hydrocarbon concentration is about 10000 ppm, good NOXIt is known that a purification rate can be obtained. Therefore, in the present invention, the predetermined range of the amplitude of the hydrocarbon concentration is set to 200 ppm to 10,000 ppm.
In addition, when the vibration period ΔT of the hydrocarbon concentration becomes long, after the hydrocarbon is supplied, the active NO isX *The surrounding oxygen concentration becomes high. In this case, when the vibration period ΔT of the hydrocarbon concentration is longer than about 5 seconds, the active NOX *Will begin to be absorbed in the
On the other hand, when the vibration period ΔT of the hydrocarbon concentration becomes approximately 0.3 seconds or less, the supplied hydrocarbon starts to accumulate on the exhaust gas flow surface of the
Next, referring to FIG. 16 to FIG.XNO when functioning as a storage catalystXThe purification method will be specifically described. In this way, the
This second NOXIn the purification method, the occluded NO occluded in the
Occlusion NOXThe amount ΣNOX is, for example, NO discharged from the engineXCalculated from the quantity. In the embodiment according to the present invention, the emission NO discharged from the engine per unit timeXThe amount NOXA is stored in advance in the
This second NOXIn the purification method, as shown in FIG. 18, the air-fuel ratio of the exhaust gas flowing into the
Well, the first NO againXReturning to the explanation of the purification method, the first NOXNO using the purification methodXAs described above, it is necessary to appropriately control the amplitude ΔH and the vibration period ΔT of the hydrocarbon concentration. That is, the first NOXNO using the purification methodXIn order to purify the gas well, the amplitude ΔH of the hydrocarbon concentration is controlled so that the air-fuel ratio (A / F) in of the exhaust gas flowing into the
In this case, in the present invention, the amplitude ΔH of the hydrocarbon concentration is controlled to control the injection amount of hydrocarbons from the
In the embodiment according to the present invention, the optimum opening degree of the
Also, the first NOXNO by purification methodXThe highest NO when the purification action is performedXAn optimum hydrocarbon injection period ΔT and an optimum hydrocarbon injection time WT that can obtain a purification rate are obtained in advance by experiments. This optimum hydrocarbon injection cycle ΔT is stored in advance in the
In FIG. 21A, the hydrocarbon injection cycle is set to the optimal hydrocarbon injection cycle ΔT shown in FIG. 20A, and the hydrocarbon injection time is set to the optimal hydrocarbon injection time WT shown in FIG. 20B. FIG. 21B shows a change in the air-fuel ratio detected by the downstream air-
Next, the structure of the upstream air-
Referring to FIG. 22A, the
By the way, SO in exhaust gasXIn this case, the air-
Next, this will be described by taking the downstream side air-
The reason is considered as follows. That is, in the air-fuel ratio sensor shown in FIG. 22A, oxygen and hydrocarbons contained in the exhaust gas diffuse in the
However, SO is in the exhaust gas.XIf this is included, this SOXAlso penetrates into the
In this case, as the amount of the sulfur component attached to the downstream air-
Therefore, in the present invention, the air-
Next, a specific method for detecting the sulfur poisoning amount of the air-
FIG. 23B shows the relationship between the reduction rate ΔAFR of the rich-side peak air-fuel ratio of the air-fuel ratio detected by the downstream air-
ΔAFR = (ΔAFp−ΔAFz) / ΔAFp
Where ΔAFp = (A / F) b− (A / F) p
ΔAFz = (A / F) b− (A / F) z
In the above equation, the base air-fuel ratio (A / F) b is determined in accordance with the operating state of the engine. On the other hand, the rich-side peak air-fuel ratio (A / F) p detected by the downstream-side air-
On the other hand, the rich-side peak air-fuel ratio (A / F) z is a value detected by the downstream-side air-
Now, if the exhaust gas contains sulfur, the peak air-fuel ratio reduction rate ΔAFR gradually increases with time, as shown by the solid line in FIG. On the other hand, the rich peak air-fuel ratio (A / F) z detected by the downstream air-
Therefore, in the embodiment according to the present invention, the downstream air-
Next, another embodiment will be described with reference to FIG. 26A. In this embodiment, the sulfur poisoning amount of the downstream air-
On the other hand, when the downstream air-
In this embodiment, in FIG. 26A, the integrated value SA of the difference between the air-fuel ratio detected by the downstream air-
That is, it can be seen that the sulfur poisoning amount of the downstream air-
Therefore, in the embodiment according to the present invention, the integral values SA and SB of the difference between the air-fuel ratio detected by the downstream air-
In this case, as the value of the integral value SA, an average value during which the air-fuel ratio varies a plurality of times can be used, and for the value of the integral value SB, an average value during which the air-fuel ratio varies a plurality of times can be used. .
Thus, the sulfur poisoning amount of the downstream air-
In this case, in the embodiment shown in FIG. 23A, the value representative of the change in the air-fuel ratio detected by the downstream air-
By the way, these reference values can be obtained in advance or can be actually measured. However, in the latter case, that is, when the reference value is actually measured, if the downstream air-
Referring to FIG. 27, when the peak air-fuel ratio reduction rate ΔAFR reaches a predetermined allowable value RX, the sulfur-poisoning recovery process of the downstream air-
As shown in FIG. 27, when the sulfur poisoning recovery process of the downstream air-
As shown in FIG. 27, when the rich-side peak air-fuel ratio (A / F) p serving as the reference value is detected, it is detected by the downstream-side air-
Further, when the amount of hydrocarbon supply from the
Now, SO in the exhaust gas2If this is included, this SO2Is oxidized on platinum Pt53 and SO3It becomes. Then this SO3Is stored in the
By the way, in this case, the temperature of the
Therefore, in the embodiment according to the present invention, the SO stored from the
On the other hand, as described above, in the present invention, the sulfur poisoning amount of the downstream air-
Next, the engine operation control routine shown in FIGS. 30 and 31 will be described. This routine is executed by interruption every predetermined time.
Referring to FIG. 30, first, at
When it is determined in
On the other hand, when it is determined at
On the other hand, when TC ≧ TCo at the time of the previous interruption, that is, when the
Second NOXNO from the purification methodXWhen switched to the purification method, NO is given to the
Now, referring to FIG. 31, first, at
In
Specifically, in
On the other hand, when it is determined at
As described above, the peak air-fuel ratio reduction rate ΔAFR is calculated based on a reference value, and this reference value can be obtained in advance or can be measured. However, when the reference value is actually measured, it is necessary to perform a sulfur poisoning recovery process for the downstream air-
Next, some examples for actually measuring this reference value will be described.
As described above, when the sulfur poisoning recovery process of the
FIG. 32 shows a routine for detecting the rich side peak air-fuel ratio (A / F) p and (A / F) z for executing this example, and this routine is executed by interruption every predetermined time.
Referring to FIG. 32, first, at
That is, it is considered that the downstream air-
On the other hand, at the time of regeneration of the
FIG. 33 shows a routine for detecting the rich-side peak air-fuel ratio (A / F) p and (A / F) z for executing this second example, and this routine is also executed by interruption every predetermined time. Is done.
Referring to FIG. 33, it is first determined in
That is, it is considered that the downstream air-
On the other hand, as described above, before the
Accordingly, in the third example, when the rich process is performed during the engine high load operation, the air-fuel ratio detected by the downstream air-
FIG. 34 shows a detection routine for the rich-side peak air-fuel ratio (A / F) p and (A / F) z for executing this third example, and this routine is also executed by interruption at regular intervals. Is done.
Referring to FIG. 34, first, at
That is, it is considered that the downstream air-
As another embodiment, an oxidation catalyst for reforming hydrocarbons can be disposed in the engine exhaust passage upstream of the
5…排気マニホルド
7…排気ターボチャージャ
12a,12b…排気管
13…排気浄化触媒
14…パティキュレートフィルタ
15…炭化水素供給弁 DESCRIPTION OF
Claims (15)
- 機関排気通路内に排気ガスの空燃比を検出するための空燃比センサを配置し、該空燃比センサにより検出された空燃比に基づいて排気浄化制御を行うようにした内燃機関の排気浄化装置において、該空燃比センサが固体電解質と、固体電解質の両側面を夫々覆う電極と、一方の電極を覆う拡散抵抗層とを有すると共に排気ガスが該拡散抵抗層上に導かれる型式のセンサからなり、排気ガスの空燃比が変化して該空燃比センサにより検出される空燃比が変化したとき、該空燃比センサにより検出される空燃比の変化が空燃比センサへの硫黄成分の付着量により左右され、このとき空燃比センサへの硫黄成分の付着量が多いほど該空燃比センサにより検出される空燃比の変化量が小さくなると共に空燃比の変化期間が長くなり、このときの空燃比センサにより検出される空燃比の変化から空燃比センサの硫黄被毒量を検出するようにした内燃機関の排気浄化装置。 In an exhaust gas purification apparatus for an internal combustion engine, an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas is disposed in an engine exhaust passage, and exhaust purification control is performed based on the air-fuel ratio detected by the air-fuel ratio sensor. The air-fuel ratio sensor comprises a solid electrolyte, a sensor of a type that has an electrode that covers both sides of the solid electrolyte, and a diffusion resistance layer that covers one of the electrodes, and exhaust gas is guided onto the diffusion resistance layer, When the air-fuel ratio of the exhaust gas changes and the air-fuel ratio detected by the air-fuel ratio sensor changes, the change in the air-fuel ratio detected by the air-fuel ratio sensor depends on the amount of sulfur component attached to the air-fuel ratio sensor. At this time, the larger the amount of sulfur component adhering to the air-fuel ratio sensor, the smaller the air-fuel ratio change amount detected by the air-fuel ratio sensor and the longer the air-fuel ratio change period. Exhaust purification system of an internal combustion engine to detect the sulfur poisoning amount of the air-fuel ratio sensor from a change in the air-fuel ratio detected by the sensor.
- 機関排気通路内に排気浄化触媒を配置し、該空燃比センサにより検出される空燃比の変化から該排気浄化触媒の硫黄被毒量を推定するようにした請求項1に記載の内燃機関の排気浄化装置。 The exhaust gas of an internal combustion engine according to claim 1, wherein an exhaust purification catalyst is disposed in the engine exhaust passage, and a sulfur poisoning amount of the exhaust purification catalyst is estimated from a change in the air-fuel ratio detected by the air-fuel ratio sensor. Purification equipment.
- 該排気浄化触媒上流の機関排気通路内に炭化水素を供給するための炭化水素供給弁を配置し、該排気浄化触媒において排気ガス中に含まれるNOXと改質された炭化水素とが反応せしめられ、該排気浄化触媒の排気ガス流通表面上には貴金属触媒が担持されていると共に該貴金属触媒周りには塩基性の排気ガス流通表面部分が形成されており、該排気浄化触媒は、排気浄化触媒に流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させると排気ガス中に含まれるNOXを還元する性質を有すると共に、該炭化水素濃度の振動周期を該予め定められた範囲よりも長くすると排気ガス中に含まれるNOXの吸蔵量が増大する性質を有しており、機関運転時に排気浄化触媒に流入する炭化水素の濃度が予め定められた範囲内の周期でもって振動するように炭化水素供給弁からの炭化水素の噴射周期が制御されると共に、排気浄化触媒に流入する炭化水素の濃度変化の振幅が予め定められた範囲内の振幅となるように炭化水素供給弁からの炭化水素の噴射量が制御される請求項2に記載の内燃機関の排気浄化装置。 A hydrocarbon supply valve for supplying hydrocarbons is arranged in the engine exhaust passage upstream of the exhaust purification catalyst, and NO X contained in the exhaust gas reacts with the reformed hydrocarbon in the exhaust purification catalyst. A noble metal catalyst is supported on the exhaust gas flow surface of the exhaust purification catalyst, and a basic exhaust gas flow surface portion is formed around the noble metal catalyst. When the concentration of the hydrocarbon flowing into the catalyst is vibrated with an amplitude within a predetermined range and a period within the predetermined range, the hydrocarbon has a property of reducing NO X contained in the exhaust gas, and the hydrocarbon the oscillation period of the concentration has a property of absorbing the amount of NO X contained in the exhaust gas to be longer than the range defined the advance is increased, hydrocarbons flowing into the exhaust purification catalyst at the time of engine operation The injection cycle of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration oscillates with a cycle within a predetermined range, and the amplitude of the change in concentration of hydrocarbons flowing into the exhaust purification catalyst is determined in advance. The exhaust emission control device for an internal combustion engine according to claim 2, wherein an injection amount of hydrocarbons from the hydrocarbon supply valve is controlled so as to have an amplitude within a predetermined range.
- 該空燃比センサが排気浄化触媒の下流に配置されており、該空燃比センサの出力信号に基づいて、排気浄化触媒に流入する炭化水素の濃度変化の振幅が予め定められた範囲内の振幅となるように炭化水素供給弁からの炭化水素の噴射量が制御される請求項3に記載の内燃機関の排気浄化装置。 The air-fuel ratio sensor is disposed downstream of the exhaust purification catalyst, and the amplitude of the change in the concentration of hydrocarbons flowing into the exhaust purification catalyst based on the output signal of the air-fuel ratio sensor is an amplitude within a predetermined range. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the injection amount of hydrocarbons from the hydrocarbon supply valve is controlled to be the same.
- 該空燃比センサが、炭化水素供給弁上流の機関排気通路内に配置された上流側空燃比センサと排気浄化触媒下流の機関排気通路内に配置された下流側空燃比センサからなり、該上流側空燃比センサの出力信号に基づいて、機関から排出される排気ガスの空燃比が予め定められた空燃比となるように機関燃焼室に供給される燃料の量が制御され、該下流側空燃比センサの出力信号に基づいて、排気浄化触媒に流入する炭化水素の濃度変化の振幅が予め定められた範囲内の振幅となるように炭化水素供給弁からの炭化水素の噴射量が制御される請求項3に記載の内燃機関の排気浄化装置。 The air-fuel ratio sensor is composed of an upstream air-fuel ratio sensor disposed in the engine exhaust passage upstream of the hydrocarbon feed valve and a downstream air-fuel ratio sensor disposed in the engine exhaust passage downstream of the exhaust purification catalyst. Based on the output signal of the air-fuel ratio sensor, the amount of fuel supplied to the engine combustion chamber is controlled so that the air-fuel ratio of the exhaust gas discharged from the engine becomes a predetermined air-fuel ratio, and the downstream air-fuel ratio is controlled. The amount of hydrocarbon injection from the hydrocarbon feed valve is controlled so that the amplitude of the change in the concentration of hydrocarbon flowing into the exhaust purification catalyst becomes an amplitude within a predetermined range based on the output signal of the sensor. Item 6. An exhaust emission control device for an internal combustion engine according to Item 3.
- 該空燃比センサが排気浄化触媒の下流に配置されており、該空燃比センサにより検出される空燃比の変化から下流側空燃比センサが硫黄被毒をしたのか或いは炭化水素供給弁が目詰まりをしたのかが判別される請求項3に記載の内燃機関の排気浄化装置。 The air-fuel ratio sensor is disposed downstream of the exhaust purification catalyst, and the downstream air-fuel ratio sensor has been poisoned by sulfur from the change in the air-fuel ratio detected by the air-fuel ratio sensor, or the hydrocarbon supply valve is clogged. The exhaust emission control device for an internal combustion engine according to claim 3, wherein whether or not it has been determined.
- 上記排気浄化触媒内において排気ガス中に含まれるNOXと改質された炭化水素とが反応して窒素および炭化水素を含む還元性中間体が生成され、上記炭化水素の噴射周期は還元性中間体を生成し続けるのに必要な周期である請求項3に記載の内燃機関の排気浄化装置。 In the exhaust purification catalyst, NO X contained in the exhaust gas reacts with the reformed hydrocarbon to produce a reducing intermediate containing nitrogen and hydrocarbons, and the injection cycle of the hydrocarbon has a reducing intermediate. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the exhaust gas purification period is a period necessary for continuously generating the body.
- 上記炭化水素の噴射周期が0.3秒から5秒の間である請求項7に記載の内燃機関の排気浄化装置。 The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the hydrocarbon injection period is between 0.3 seconds and 5 seconds.
- 上記貴金属触媒は白金Ptと、ロジウムRhおよびパラジウムPdの少なくとも一方とにより構成される請求項3に記載の内燃機関の排気浄化装置。 The exhaust purification device for an internal combustion engine according to claim 3, wherein the noble metal catalyst is composed of platinum Pt and at least one of rhodium Rh and palladium Pd.
- 上記排気浄化触媒の排気ガス流通表面上にアルカリ金属又はアルカリ土類金属又は希土類又はNOXに電子を供与しうる金属を含む塩基性層が形成されており、該塩基性層の表面が上記塩基性の排気ガス流通表面部分を形成している請求項3に記載の内燃機関の排気浄化装置。 The basic layer comprising a metal which can donate electrons to the alkali metal or alkaline earth metal or rare earth or NO X in the exhaust gas flow on the surface of the exhaust purification catalyst is formed, the surface of the base layer is the base The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the exhaust gas circulation surface portion is formed.
- 該空燃比センサが排気浄化触媒の下流に配置されており、硫黄被毒を生じていないときの該空燃比センサにより検出される空燃比の変化を代表する値が基準値として予め求められており、この基準値に対する、該空燃比センサにより検出された空燃比の変化を代表する値から空燃比センサの硫黄被毒量を検出するようにした請求項1に記載の内燃機関の排気浄化装置。 The air-fuel ratio sensor is disposed downstream of the exhaust purification catalyst, and a value representative of a change in the air-fuel ratio detected by the air-fuel ratio sensor when no sulfur poisoning occurs is obtained in advance as a reference value. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the sulfur poisoning amount of the air-fuel ratio sensor is detected from a value representative of a change in the air-fuel ratio detected by the air-fuel ratio sensor with respect to the reference value.
- 該空燃比センサにより検出される空燃比の変化を代表する値がリッチ側ピーク空燃比である請求項11に記載の内燃機関の排気浄化装置。 The exhaust gas purification apparatus for an internal combustion engine according to claim 11, wherein a value representative of a change in the air-fuel ratio detected by the air-fuel ratio sensor is a rich-side peak air-fuel ratio.
- 該空燃比センサにより検出される空燃比とベース空燃比との差の積分値が算出されており、排気ガスの空燃比が瞬時的に変化したときに該空燃比センサにより検出される空燃比は、空燃比センサが硫黄被毒をしていなければ予め定められた期間内で瞬時的に変化を完了するが空燃比センサの硫黄被毒量が増大すると該予め定められた期間を超えて変化し続け、空燃比センサにより検出される空燃比の変化を代表する値が該予め定められた期間内における該積分値と該予め定められた期間を超えているときの該積分値との比である請求項11に記載の内燃機関の排気浄化装置。 The integral value of the difference between the air-fuel ratio detected by the air-fuel ratio sensor and the base air-fuel ratio is calculated, and the air-fuel ratio detected by the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas changes instantaneously is If the air-fuel ratio sensor is not poisoned with sulfur, the change is instantaneously completed within a predetermined period, but if the amount of sulfur poisoning of the air-fuel ratio sensor increases, it changes beyond the predetermined period. Subsequently, the value representative of the change in the air-fuel ratio detected by the air-fuel ratio sensor is the ratio between the integral value within the predetermined period and the integral value when exceeding the predetermined period. The exhaust emission control device for an internal combustion engine according to claim 11.
- 上記基準値は、排気ガス温が上昇せしめられ或いは排気ガスの空燃比がリッチにされ或いはそれらの双方により空燃比センサの硫黄被毒が回復されたときに検出される請求項11に記載の内燃機関の排気浄化装置。 12. The internal combustion engine according to claim 11, wherein the reference value is detected when the exhaust gas temperature is raised, the air-fuel ratio of the exhaust gas is made rich, or when sulfur poisoning of the air-fuel ratio sensor is recovered by both of them. Engine exhaust purification system.
- 該空燃比センサにより検出される空燃比の変化を代表する値を求めるときには、排気ガスの空燃比のリッチ側ピーク空燃比が更にリッチ側とされる請求項11に記載の内燃機関の排気浄化装置。 12. The exhaust emission control device for an internal combustion engine according to claim 11, wherein when obtaining a value representative of a change in the air-fuel ratio detected by the air-fuel ratio sensor, the rich-side peak air-fuel ratio of the exhaust gas is made richer. .
Priority Applications (7)
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JP2012505926A JP5246375B1 (en) | 2011-08-01 | 2011-08-01 | Exhaust gas purification device for internal combustion engine |
EP11826106.4A EP2574748B1 (en) | 2011-08-01 | 2011-08-01 | Exhaust purifying method for internal combustion engine |
ES11826106.4T ES2628816T3 (en) | 2011-08-01 | 2011-08-01 | Exhaust gas purification method for an internal combustion engine |
US13/499,331 US8707680B2 (en) | 2011-08-01 | 2011-08-01 | Exhaust purification system of internal combustion engine |
BR112013006135-9A BR112013006135B1 (en) | 2011-08-01 | 2011-08-01 | internal combustion engine discharge purification system |
CN201180004041.2A CN103026022B (en) | 2011-08-01 | 2011-08-01 | Exhaust purification system of internal combustion engine |
PCT/JP2011/067998 WO2013018234A1 (en) | 2011-08-01 | 2011-08-01 | Exhaust purifying apparatus for internal combustion engine |
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Also Published As
Publication number | Publication date |
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EP2574748A8 (en) | 2013-06-19 |
JPWO2013018234A1 (en) | 2015-03-05 |
EP2574748A1 (en) | 2013-04-03 |
JP5246375B1 (en) | 2013-07-24 |
BR112013006135A2 (en) | 2020-08-04 |
CN103026022B (en) | 2015-05-20 |
ES2628816T3 (en) | 2017-08-04 |
EP2574748A4 (en) | 2015-03-04 |
US20130034468A1 (en) | 2013-02-07 |
CN103026022A (en) | 2013-04-03 |
EP2574748B1 (en) | 2017-05-03 |
US8707680B2 (en) | 2014-04-29 |
BR112013006135B1 (en) | 2021-02-09 |
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